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Keywords:

  • physical activity;
  • prostate;
  • cancer;
  • epidemiology

Abstract

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Conflict of Interest Disclosures
  7. References

BACKGROUND:

The relation of physical activity across the lifespan to risk of prostate cancer has not been thoroughly investigated, particularly among black men. The authors investigated physical activity, including activity during different age periods and of various intensities, in relation to prostate cancer incidence among white men and black men.

METHODS:

In total, 160,006 white men and 3671 black men ages 51 years to 72 years who were enrolled in the National Institutes of Health-AARP Diet and Health Study reported their time spent per week engaging in physical activity during ages 15 to 18 years, 19 years to 29 years, 35 years to 39 years, and during the past 10 years. Cox regression models were used to examine physical activity, categorized by intensity (moderate or vigorous, light, and total), in relation to prostate cancer risk.

RESULTS:

During 7 years of follow-up, 9624 white men and 371 black men developed prostate cancer. Among white men, physical activity had no association with prostate cancer regardless of age period or activity intensity. Among black men, engaging in ≥4 hours of moderate/vigorous intensity physical activity versus infrequent activity during ages 19 years to 29 years was related to a 35% lower risk of prostate cancer (relative risk, 0.65; 95% confidence interval [95% CI], 0.43-0.99 [Ptrend = .01]). Frequent moderate/vigorous physical activity at ages 35 years to 39 years also potentially was related to reduced prostate cancer risk (relative risk, 0.59; 95% CI, 0.36-0.96 [Ptrend = .15]).

CONCLUSIONS:

Regular physical activity may reduce prostate cancer risk among black men, and activity during young adulthood may yield the greatest benefit. This novel finding needs confirmation in additional studies. Cancer 2009. Published 2009 by the American Cancer Society.

Physical activity, or lack thereof, has been proposed as a modifiable risk factor for prostate cancer. In randomized exercise trials, physical activity increases levels of sex hormone-binding globulin (SHBG)1 and SHBG levels, in turn, have been related to modest reductions in prostate cancer risk.2 However, despite a biologically plausible relation, a recent systematic review of 38 epidemiologic studies indicated that physical activity was associated inconsistently with prostate cancer risk.3 The review also noted that, to resolve these inconsistent findings, it is necessary to conduct further large-scale etiologic studies that assess the physical activity and prostate cancer relation among racial/ethnic minorities, such as black men, and to examine physical activity over the entire lifespan. To our knowledge to date, only 3 studies have examined physical activity in relation to prostate cancer among black men,4-6: One prospective study indicated a 3-fold risk of prostate cancer among inactive black men,4 and 2 case-control studies indicated no association.5, 6 Four studies have examined physical activity over the entire lifespan in relation to prostate cancer,7-11 and no strong evidence has emerged for a protective effect of physical activity during earlier life.

To assess whether the association between physical activity and prostate cancer varies by race/ethnicity and age period, we prospectively examined physical activity, according to age period and physical activity intensity, in relation to prostate cancer among ≈165,000 white and black men who were enrolled in the National Institutes of Health (NIH)-AARP Diet and Health Study.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Conflict of Interest Disclosures
  7. References

Study Population

The NIH-AARP Diet and Health Study was established in 1995/1996, when 566,402 AARP members who resided in 1 of 6 states (California, Florida, Pennsylvania, New Jersey, North Carolina, and Louisiana) or in 2 metropolitan areas (Atlanta, Georgia and Detroit, Michigan) responded to a questionnaire soliciting information on demographic traits, physical activity, and other health-related behaviors. The selection of these sites was based on the presence of high-quality cancer registries, minority representation, and large AARP memberships.12 To those who responded to the baseline questionnaire and who did not have a self-reported history of prostate, breast, or colorectal cancer, we mailed a second questionnaire within 6 months requesting further information on physical activity and other lifestyle factors. Participants in the current study responded to both questionnaires and were alive and had not moved from the study area before returning their second questionnaire (N = 334,908). We excluded participants whose questionnaires were completed by proxy (n = 10,383), women (n = 136,408), individuals with a self-reported prevalent cancer (n = 7396), individuals who had any cancer diagnosis before the second questionnaire (n = 2157), and individuals who were missing physical activity data (n = 7992). We excluded men who were neither black (African-American) nor white (Caucasian) because of small case numbers (there were only 153 cases among Hispanics and 104 cases among Asians/Pacific Islanders). In total, our analytic cohort consisted of 160,006 white men and 3671 black men ages 51 years to 72 years at the start of our follow-up.

The NIH-AARP Diet and Health Study was approved by the Special Studies Institutional Review Board of the National Cancer Institute. All participants provided written informed consent.

Assessment of Physical Activity

On the second questionnaire, participants were asked to report the amount of time spent engaging in moderate/vigorous activities (eg, biking, fast walking, aerobics, and jogging/running) and light activities (eg, light housework, slow walking, and light gardening) at ages 15 years to 18 years, ages 19 years to 29 years, ages 35 years to 39 years, and during the past 10 years. In a published compendium, our examples of moderate-intensity activity and light-intensity activity corresponded approximately to metabolic equivalent (MET) values of 5 and 3, respectively.13 Participants selected their level of activity from 6 pre-established response options: never, rarely, weekly but <1 hour per week, 1 to 3 hours per week, 4 to 7 hours per week, and >7 hours per week (ie, “frequent activity”).

To assess total physical activity at each age, we calculated age-specific indices of physical activity using the formula: moderate/vigorous activity*5 METs + light physical activity*3 METs. We also calculated an overall lifetime total physical activity index by averaging the age-specific physical activity indices.

Ascertainment and Classification of Prostate Cancer Cases

Incident, first primary prostate cancer cases (International Classification of Diseases ninth version, Rubric 185 or 10th version, Rubric C61) were identified through December 31, 2003 by linking NIH-AARP cohort data with the 8 state cancer registries that served our cohort and 3 additional states (Arizona, Nevada, and Texas). In a previous validation study, the sensitivity of cancer identification in our cohort was estimated at ≈90%, and the specificity was 99.5%.14 Deaths from prostate cancer also were identified through linkage to the National Death Index Plus.

Statistical Analysis

Participants were followed from the date of return of the second questionnaire in late 1996 until the diagnosis of first cancer, a move from the cancer registry ascertainment areas, death, or the date of last follow-up on December 31, 2003. Thus, the participants were followed for a maximum of 7 years, and most (74%) still were being followed as of the end of 2003. Relative risks (RR) and 95% confidence intervals (95% CIs) for prostate cancer were estimated using proportional hazards regression. In analyses of moderate/vigorous activity and light activity, the bottom 2 categories of physical activity (ie, “never” and “rarely” engaging in moderate/vigorous or light physical activity) were collapsed into a new category (“infrequent” physical activity) to ensure sufficient numbers of cases in the reference category. For lifetime physical activity analyses, participants were categorized according to approximate quintiles of total MET-hours per week (ie, ≤11.5 MET-hours per week, 11.6‒26.5 MET-hours per week, 26.6‒41.5 MET-hours per week, 41.6‒51.5 MET-hours per week, and ≥51.6 MET-hours per week). The same groupings were used for each age-specific physical activity analysis. For tests of trend, each moderate/vigorous physical activity category was assigned a single value that indicated the approximate number of hours of activity per week (never/rarely = 0.125, weekly but <1 hour per week = 0.5, 1-3 hours per week = 2, 4-7 hours per week = 5.5, and >7 hours per week = 8).

Covariates were included in multivariate models if prior studies consistently identified an association with prostate cancer or if the covariate was a statistically significant predictor of prostate cancer in this cohort. In addition, models for ages 15 years to 18 years, ages 19 years to 29 years, and ages 35 years to 39 years were adjusted for moderate/vigorous physical activity and light physical activity during the past 10 years. For covariates for which information was not complete, we assigned a missing indicator variable to model the nonresponse.

Linear trend tests were conducted using the midpoint value of each physical activity category (eg, for the category of 1 to 3 hours of activity per week, a value of 2 hours was assigned). We formally tested for interactions of the physical activity and prostate cancer association by using the likelihood ratio test, ie, comparing the likelihood of models with and without multiplicative interaction terms. Interaction terms were calculated as the cross-product of physical activity, which was modeled as a continuous variable using category midpoints, and the factor of interest (eg, race). Tests of the proportional hazards assumption did not reveal any departure from proportionality.

All P values were based on 2-sided tests with an α of .05. Analyses were performed using Statistical Analysis System (SAS) statistical software (release 9.1.3; SAS Institute Inc, Cary, NC).

RESULTS

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Conflict of Interest Disclosures
  7. References

During up to 7 years of follow-up, 9624 prostate cancer cases were identified in white men, and 371 cases were identified in black men. Physical activity levels were correlated across the lifespan with strong correlations (>0.7) between adjacent age periods and with moderate-to-weak correlations between nonadjacent age periods. The pairwise correlation coefficients of total physical activity during ages 15 years to 18 years with physical activity during ages 19 years to 29 years, during ages 35 years to 39 years, and during the past 10 years were 0.75, 0.56, and 0.31, respectively. Similar patterns of correlation were observed among white men and black men alike. The respondents to our questionnaire were more educated than the general population, because 48% of white men and 36% of black men had at least a college degree compared with 19% of white men and 6% of black men of the same age range in the general population.15

The baseline characteristics among the least active and most active white and black members of our cohort are listed in Table 1. Frequent physical activity during ages 15 years to 18 years and during ages 19 years to 29 years was not related to participant demographics, lifestyle factors, or screening habits among either white men or black men. In contrast, frequent physical activity during ages 35 years to 39 years and during the past 10 years was related to many participant factors, including more frequent rectal and prostate-specific antigen (PSA) examinations, a lower body mass index (BMI), a lower likelihood of diabetes, and a greater dietary lycopene intake. Among black men, physical activity during the past 10 years also was related to a family history of prostate cancer (10.1% in active black men vs 7.6% in inactive black men). The proportion of men who engaged in the highest level of activity at ages 15 years to 18 years was slightly greater among blacks (37%) than among whites (33%). In contrast, the proportion of men who engaged in the highest level of activity during the most recent 10 years was lower among blacks (14%) than among whites (19%).

Table 1. Demographic and Lifestyle Characteristics Among Those Participants Who Were Least and Most Active During Ages 15 Years to 18 Years, 19 Years to 29 Years, and 35 Years to 39 Years, and Within the Past 10 Years
CharacteristicLevel of Physical Activity
Ages 15-18 YearsAges 19-29 YearsAges 35-39 YearsWithin Past 10 Years
Least Active*Most ActiveLeast ActiveMost ActiveLeast ActiveMost ActiveLeast ActiveMost Active
  • PSA indicates prostate-specific antigen; BMI, body mass index.

  • *

    Participants who were the least active were those who engaged in less than the equivalent of 11.5 metabolic equivalent (MET)-hours (MET-h) per week of light, moderate, and/or vigorous activity combined. Participants who were the most active were those who engaged in ≥51.6 MET-h of light, moderate, and/or vigorous activity.

White men        
 No. of participants24,53153,19228,84840,29833,48329,84232,90329,988
 Mean age, y63.163.162.863.462.863.562.463.8
 Family history of prostate cancer, %8.598.88.88.78.88.58.9
 Rectal examination during past 3 y, %        
  None14.614.71415.214.8151713.6
  Once27.92727.3272826.829.825.2
  More than once57.558.358.757.757.258.353.261.2
 PSA blood test during past 3 y, %        
  None22.822.822.223.523.123.326.221
  Once26.426.42626.226.226.128.224.9
  More than once50.850.851.750.350.750.645.654.1
 Mean BMI, kg/m226.927.426.927.427.327.128.226.4
 History of diabetes, %9.79.69.79.411.28.513.17.1
 Mean Lycopene intake, μg/d73518035735981097388815874318182
Black men        
 No. of participants589134464710529556731185499
 Mean Age, y62.261.46261.661.661.661.561.8
 Family history of prostate cancer, %9.68.599.28.897.610.1
 Rectal examination during past 3 y, %        
  None14.913.516.213.217.813.219.611.6
  Once30.426.530.425.429.524.930.525
  More than once54.759.953.461.452.761.949.863.4
 PSA blood test during past 3 y, %        
  None26.324.425.424.92623.828.218.4
  Once30.527.530.227.230.225.732.526.9
  More than once43.24844.447.943.850.439.354.7
 Mean BMI, kg/m228.22828.227.928.427.528.726.9
 History of diabetes, %2017.319.417.62115.52014.4
 Mean Lycopene intake, μg/d57286083550962165485661054176271

Table 2 displays the association of moderate/vigorous physical activity during different age periods with prostate cancer risk. Among white men, there was no association between time spent in physical activity of a moderate/vigorous intensity and incidence of prostate cancer, regardless of the age period examined (all Ptrend>.05). For frequent moderate/vigorous physical activity during ages 15 years to 18 years, the 95% CI excluded 1 (95% CI, 1.01-1.21), but the trend was not statistically significant (Ptrend = .80).

Table 2. Relative Risks of Prostate Cancer Related to Moderate/Vigorous Physical Activity by Age Period
Age PeriodFrequency of Moderate/Vigorous Physical Activity: RR (95% CI)
InfrequentWeekly, <1 Hour/Week1 to 3 Hours/Week4 to 7 Hours/Week>7 Hours/WeekPTrend
  • RR indicates relative risk; 95% CI, 95% confidence interval; Ref, referent group.

  • *

    Multivariate models were adjusted for age at baseline; age-squared; history of digital rectal examination within the past 3 years (none, once, and more than once); history of prostate-specific antigen examination within the past 3 years (none, once, and more than once); body mass index at baseline (<25 kg/m2, 25-29.9 kg/m2, 30.0-34.9 kg/m2, 35.0-39.9 kg/m2, and ≥40 kg/m2); body mass index at age 18 years (<25 kg/m2, 25-29.9 kg/m2, 30.0-34.9 kg/m2, 35.0-39.9 kg/m2, and ≥40 kg/m2); waist circumference (<35 inches, 35-38 inches, 39-41 inches, 42-44 inches, and ≥44 inches); history of diabetes (yes/no); highest level of education (did not complete high school, completed high school, some college, or completed college and/or graduate school); marital status (married, divorced, separated, widowed, or unmarried); smoking history (current smoker, former smoker, or nonsmoker); family history of prostate cancer (yes/no); multivitamin use (yes/no); supplemental zinc use (yes/no); alcohol intake (quintiles); and quintiles of energy-adjusted intakes of red meat, processed meats, α-linolenic acid, gamma-tocopherol, lycopene, fish, calcium (from the combination of food and supplements), and vitamin D (from the combination of food and supplements). In addition, models for ages 15-18 years, 19-29 years, and 35-39 years were adjusted for light physical activity during each of the respective periods and for moderate/vigorous physical activity and light physical activity during the past 10 years. Models for physical activity during the past 10 years were not adjusted for physical activity during earlier ages but were adjusted for light physical activity during the same period.

White men      
 Ages 15-18 y      
  No. of cases627512162821044753 
  Age-adjusted RR 1 (Ref)1.13 (1.01-1.27)1.16 (1.06-1.27)1.15 (1.05-1.26)1.14 (1.05-1.24).23
  Multivariate RR*1 (Ref)1.12 (0.99-1.26)1.15 (1.05-1.27)1.13 (1.03-1.24)1.11 (1.01-1.21).80
 Ages 19-29 y      
  No. of cases744755214627193260 
  Age-adjusted RR1 (Ref)1.03 (0.93-1.14)1.03 (0.95-1.12)1.04 (0.96-1.13)1.00 (0.93-1.09).58
  Multivariate RR1 (Ref)1.01 (0.91-1.12)1.02 (0.93-1.11)1.01 (0.93-1.11)0.97 (0.89-1.07).28
 Ages 35-39 y      
  No. of cases915950258527552419 
  Age-adjusted RR1 (Ref)0.96 (0.88-1.06)1.01 (0.94-1.09)1.00 (0.93-1.08)1.01 (0.94-1.09).55
  Multivariate RR1 (Ref)0.95 (0.86-1.04)0.99 (0.90-1.08)0.96 (0.87-1.05)0.98 (0.88-1.08).73
 Past 10 y      
  No. of cases1213926236526202500 
  Age-adjusted RR1 (Ref)1.02 (0.93-1.11)1.06 (0.99-1.14)1.11 (1.04-1.19)1.09 (1.02-1.17).003
  Multivariate RR1 (Ref)0.99 (0.90-1.08)1.01 (0.94-1.09)1.04 (0.97-1.12)1.03 (0.96-1.11).19
Black men      
 Ages 15-18 y      
  No. of cases39206071181 
  Age-adjusted RR1 (Ref)0.82 (0.48-1.41)0.81 (0.54-1.21)0.81 (0.54-1.19)0.84 (0.59-1.19).71
  Multivariate RR1 (Ref)0.84 (0.48-1.47)0.81 (0.52-1.24)0.74 (0.48-1.14)0.78 (0.52-1.17).39
 Ages 19-29 y      
  No. of cases40357392131 
  Age-adjusted RR1 (Ref)1.09 (0.69-1.72)0.80 (0.55-1.18)0.74 (0.51-1.07)0.80 (0.56-1.14).13
  Multivariate RR1 (Ref)1.12 (0.69-1.83)0.78 (0.51-1.21)0.61 (0.40-0.95)0.67 (0.43-1.05).02
 Ages 35-39 y      
  No. of cases56359010684 
  Age-adjusted RR1 (Ref)0.75 (0.49-1.15)0.82 (0.59-1.15)0.97 (0.70-1.34)0.87 (0.62-1.22).74
  Multivariate RR1 (Ref)0.75 (0.47-1.20)0.69 (0.45-1.04)0.69 (0.45-1.07)0.59 (0.36-0.96).15
 Past 10 y      
  No. of cases7336979768 
  Age-adjusted RR1 (Ref)0.81 (0.54-1.21)1.14 (0.84-1.54)1.26 (0.93-1.70)1.20 (0.86-1.67).06
  Multivariate RR1 (Ref)0.76 (0.50-1.16)1.14 (0.81-1.61)1.34 (0.94-1.91)1.28 (0.85-1.92).04

Among black men, moderate/vigorous physical activity during specific age periods was related to prostate cancer risk, with the benefit most evident for activity during ages 19 years to 29 years (Table 2). The multivariate RRs of prostate cancer for frequent versus infrequent moderate/vigorous physical activity performed during specific ages were as follows: For ages 15 years to 18 years, the RR was 0.78 (95% CI, 0.52-1.17; Ptrend = .39); for ages 19 years to 29 years, the RR was 0.67 (95% CI, 0.43-1.05; Ptrend = .02); for ages 35 years to 39 years, the RR was 0.59 (95% CI, 0.36-0.96; Ptrend = .15); and, for activity during the past 10 years, the RR was 1.28 (95% CI, 0.85-1.92; Ptrend = .04). Because the results for moderate/vigorous physical activity during ages 19 years to 29 years suggested a potential threshold effect, we reanalyzed the data by grouping the 2 highest activity levels. In this reanalysis, the RR for engaging in ≥4 hours per week of moderate/vigorous physical activity versus infrequent activity was 0.65 (95% CI, 0.43-0.99; Ptrend = .01). We also examined whether the association between moderate/vigorous physical activity during ages 19 years to 29 years and prostate cancer differed between white men and black men, but the difference had only borderline statistical significance (Pinteraction = .10). Among black men, moderate/vigorous activity during the past 10 years was associated modestly with increased prostate cancer risk (Ptrend = .04), but the point estimates for distinct physical activity categories were not statistically significant.

In Table 3, we indicate that physical activity of a light intensity was not related to prostate cancer risk among either white men or black men (all Ptrend>.05). Among white men, the multivariate RRs of prostate cancer for frequent versus infrequent light physical activity during ages 15 years to 18 years, ages 19 years to 29 years, ages 35 years to 39 years, and during the past 10 years were 0.97, 0.95, 0.91, and 0.96, respectively. Among black men, the corresponding multivariate RRs were 0.99, 0.96, 1.25, and 0.84, respectively.

Table 3. Relative Risks of Prostate Cancer Related to Light Physical Activity by Age Period
Age PeriodFrequency of Light Physical Activity: RR (95% CI)
InfrequentWeekly, <1 Hour/Week1 to 3 Hours/Week4 to 7 Hours/Week>7 Hours/WeekPTrend
  • RR indicates relative risk; 95% CI, 95% confidence interval; Ref, referent group.

  • *

    Multivariate models were adjusted for the covariates indicated in Table 2. In addition, models for ages 15 to 18 years, 19 to 29 years, and 35 to 39 years were adjusted for moderate/vigorous physical activity during each of the respective periods and for light physical activity and moderate/vigorous physical activity during the past 10 years. Models for physical activity during the past 10 years were not adjusted for physical activity during earlier ages but were adjusted for light physical activity during the same period.

White men      
 Ages 15-18 y      
  No. of cases1695860213117383200 
  Age-adjusted RR 1 (Ref)1.00 (0.92-1.09)0.99 (0.93-1.06)0.94 (0.88-1.01)0.97 (0.92-1.03).19
  Multivariate RR*1 (Ref)0.98 (0.90-1.07)0.97 (0.90-1.03)0.92 (0.86-0.99)0.97 (0.91-1.04).33
 Ages 19-29 y      
  No. of cases1235958238023182733 
  Age-adjusted RR1 (Ref)1.00 (0.92-1.09)0.95 (0.88-1.01)0.94 (0.88-1.01)0.94 (0.88-1.01).06
  Multivariate RR1 (Ref)0.98 (0.90-1.07)0.93 (0.86-0.99)0.92 (0.85-1.00)0.95 (0.87-1.03).46
 Ages 35-39 y      
  No. of cases1062982261225662402 
  Age-adjusted RR1 (Ref)0.99 (0.91-1.08)0.93 (0.87-1.00)0.93 (0.86-1.00)0.94 (0.88-1.01).13
  Multivariate RR1 (Ref)0.98 (0.89-1.08)0.90 (0.82-0.98)0.89 (0.81-0.97)0.91 (0.82-1.01).17
 Past 10 y      
  No. of cases1213926236526202500 
  Age-adjusted RR1 (Ref)0.98 (0.89-1.08)1.01 (0.93-1.09)1.02 (0.94-1.10)1.01 (0.94-1.09).50
  Multivariate RR1 (Ref)0.97 (0.88-1.07)0.98 (0.91-1.06)0.97 (0.90-1.05)0.96 (0.89-1.04).33
Black men      
 Ages 15-18 y      
  No. of cases61277973131 
  Age-adjusted RR1 (Ref)1.03 (0.65-1.62)0.94 (0.67-1.31)1.06 (0.76-1.49)0.92 (0.68-1.24).66
  Multivariate RR1 (Ref)1.07 (0.66-1.72)1.00 (0.70-1.44)1.18 (0.81-1.72)0.99 (0.70-1.41).94
 Ages 19-29 y      
  No. of cases493581101105 
  Age-adjusted RR1 (Ref)0.93 (0.60-1.43)0.86 (0.60-1.22)0.98 (0.69-1.37)0.83 (0.59-1.17).53
  Multivariate RR1 (Ref)0.95 (0.60-1.50)0.95 (0.64-1.42)1.17 (0.78-1.74)0.96 (0.63-1.47).70
 Ages 35-39 y      
  No. of cases4939969988 
  Age-adjusted RR1 (Ref)0.91 (0.60-1.38)0.91 (0.64-1.28)1.03 (0.73-1.46)1.00 (0.71-1.42).51
  Multivariate RR1 (Ref)0.89 (0.56-1.43)1.02 (0.67-1.55)1.22 (0.78-1.91)1.25 (0.76-2.06).14
 Past 10 y      
  No. of cases54451068284 
  Age-adjusted RR1 (Ref)1.17 (0.79-1.74)1.07 (0.77-1.48)0.98 (0.70-1.39)1.09 (0.78-1.54).94
  Multivariate RR1 (Ref)1.18 (0.78-1.79)0.92 (0.64-1.32)0.78 (0.53-1.15)0.84 (0.56-1.26).13

Table 4 indicates the association between total physical activity (ie, moderate/vigorous and light activity combined) during different age periods and the risk of prostate cancer. Total physical activity was not related to prostate cancer risk among white men (all Ptrend>.05). Among black men, total physical activity during ages 19 years to 29 years was associated with a modest reduction in the risk of prostate cancer (high vs low total physical activity; hazard ratio, 0.75; Ptrend = .045). This association likely reflects vigorous physical activity, because light physical activity was unrelated to prostate cancer risk.

Table 4. Relative Risks of Prostate Cancer Related to Metabolic Equivalent Hours of Physical Activity Per Week by Age Period
Age PeriodMET-h of Physical Activity Per Week: RR (95% CI)
≤11.511.6 to 26.526.6 to 41.541.6 to 51.5≥51.6PTrend
  • MET-h indicates metabolic equivalent-hours; RR, relative risk; 95% CI, 95% confidence interval; Ref, referent group.

  • *

    Multivariate models were adjusted for the covariates indicated in Table 2. In addition, models for ages 15 to 18 years, 19 to 29 years, and 35 to 39 years were adjusted for total physical activity during the past 10 years.

White men      
 Ages 15-18 y      
  No. of cases14171192210517133197 
  Age-adjusted RR1 (Ref)1.07 (0.99-1.15)1.08 (1.00-1.15)1.04 (0.97-1.11)1.04 (0.98-1.11).67
  Multivariate RR*1 (Ref)1.05 (0.97-1.14)1.03 (0.96-1.10)1.00 (0.93-1.08)1.02 (0.95-1.09).88
 Ages 19-29 y      
  No. of cases17261717179819652418 
  Age-adjusted RR1 (Ref)0.99 (0.93-1.06)1.04 (0.97-1.11)0.97 (0.91-1.03)0.97 (0.91-1.03).16
  Multivariate RR1 (Ref)0.98 (0.91-1.05)1.00 (0.93-1.07)0.94 (0.88-1.01)0.95 (0.88-1.01).06
 Ages 35-39 y      
  No. of cases20102201152320261864 
  Age-adjusted RR1 (Ref)0.97 (0.91-1.03)1.00 (0.94-1.07)0.96 (0.90-1.02)0.99 (0.93-1.05).67
  Multivariate RR1 (Ref)0.93 (0.88-1.00)0.94 (0.87-1.01)0.91 (0.84-0.97)0.95 (0.88-1.03).12
 Past 10 y      
  No. of cases17492336152420971918 
  Age-adjusted RR1 (Ref)1.05 (0.99-1.12)1.13 (1.05-1.21)1.10 (1.03-1.17)1.07 (1.00-1.14).02
  Multivariate RR1 (Ref)1.02 (0.95-1.08)1.06 (0.99-1.13)1.03 (0.97-1.10)1.01 (0.94-1.08).71
 Lifetime activity, averaged      
  No. of cases8082172290217461996 
  Age-adjusted RR1 (Ref)1.01 (0.93-1.09)1.03 (0.96-1.12)1.01 (0.93-1.10)1.02 (0.94-1.11).66
  Multivariate RR1 (Ref)0.98 (0.90-1.06)0.99 (0.91-1.07)0.97 (0.89-1.05)0.98 (0.90-1.06).59
Black men      
 Ages 15-18 y      
  No. of cases64526060135 
  Age-adjusted RR1 (Ref)1.00 (0.70-1.45)0.84 (0.59-1.19)0.95 (0.67-1.36)0.93 (0.69-1.26).69
  Multivariate RR1 (Ref)0.99 (0.67-1.44)0.74 (0.51-1.07)0.89 (0.61-1.28)0.85 (0.62-1.17).36
 Ages 19-29 y      
  No. of cases72666070103 
  Age-adjusted RR1 (Ref)0.95 (0.68-1.33)0.92 (0.65-1.30)0.82 (0.59-1.14)0.87 (0.64-1.17).25
  Multivariate RR1 (Ref)0.93 (0.66-1.31)0.81 (0.57-1.16)0.72 (0.51-1.02)0.75 (0.54-1.05).045
 Ages 35-39 y      
  No. of cases9281488268 
  Age-adjusted RR1 (Ref)0.98 (0.73-1.32)1.02 (0.72-1.44)1.17 (0.87-1.58)1.02 (0.75-1.40).53
  Multivariate RR1 (Ref)0.93 (0.68-1.27)0.86 (0.59-1.26)1.01 (0.72-1.42)0.91 (0.62-1.35).84
 Past 10 y      
  No. of cases10393497551 
  Age-adjusted RR1 (Ref)1.11 (0.84-1.47)1.35 (0.96-1.90)1.33 (0.99-1.79)1.12 (0.80-1.56).15
  Multivariate RR1 (Ref)1.04 (0.78-1.39)1.26 (0.89-1.79)1.27 (0.94-1.73)1.06 (0.75-1.50).29
 Lifetime activity, averaged      
  No. of cases5380986575 
  Age-adjusted RR1 (Ref)0.80 (0.56-1.13)0.73 (0.52-1.02)0.85 (0.59-1.22)0.94 (0.66-1.33).90
  Multivariate RR1 (Ref)0.76 (0.53-1.08)0.69 (0.49-0.97)0.78 (0.54-1.13)0.88 (0.61-1.27).85

To further explore the association between moderate/vigorous intensity physical activity during young adulthood and prostate cancer among black men, Table 5 provides data from our analyses stratified according to age at baseline (<65 years vs ≥65 years), age at diagnosis (<65 years vs ≥65 years), and BMI at baseline (<25 kg/m2 vs ≥25 kg/m2). Among black men aged <65 years at baseline, frequent moderate/vigorous physical activity during young adulthood was related to a 56% reduced risk of prostate cancer relative to infrequent exercise at this age (RR, 0.44; 95% CI, 0.26-0.76 [Ptrend<.01; Pinteraction = .03]). Similar but somewhat less robust findings were produced in the analyses of prostate cancers diagnosed before age 65 years (RR, 0.43; 95% CI, 0.21-0.88 [Ptrend = .09]). For black men who had a BMI <25 kg/m2 at baseline, frequent moderate/vigorous physical activity was related to a 57% reduction in prostate cancer risk among active men (RR, 0.43; 95% CI, 0.18-1.00 [Ptrend = .02; Pinteraction = .08]).

Table 5. Relative Risks of Prostate Cancer Related to Moderate/Vigorous Physical Activity at Ages 19 to 29 Years Among Black Men*
VariableFrequency of Moderate/Vigorous Physical Activity at Ages 19 to 29 Years: RR (95% CI)
InfrequentWeekly, <1 Hour/Week1-3 Hours/Week4-7 Hours/Week>7 Hours/WeekPTrend
  • RR indicates relative risk; 95% CI, confidence interval; Ref, referent group; BMI, body mass index.

  • *

    Pinteraction for age at baseline=.03; Pinteraction for BMI=.08.

  • Multivariate models were adjusted for age at baseline, age-squared, history of digital rectal examination during the past 3 years (none, once, and more than once), history of prostate-specific antigen examination during the past 3 years (none, once, and more than once), BMI at baseline (<25 kg/m2, 25-29.9 kg/m2, 30.0-34.9 kg/m2, 35.0-39.9 kg/m2, and ≥40 kg/m2), BMI at age 18 years (<25 kg/m2, 25-29.9 kg/m2, 30.0-34.9 kg/m2, 35.0-39.9 kg/m2, and ≥40 kg/m2), smoking history (current smoker, former smoker, or nonsmoker), family history of prostate cancer (yes/no), quintiles of energy-adjusted intakes of gamma-tocopherol and calcium (from the combination of food and supplements), light physical activity during ages 19 to 29 years, moderate/vigorous physical activity during the past 10 years, and light physical activity during the past 10 years.

Age at baseline, y      
 <65      
  No. of cases2823496485 
  Age-adjusted RR 1 (Ref)0.93 (0.53-1.61)0.65 (0.41-1.04)0.62 (0.40-0.96)0.62 (0.40-0.96).048
  Multivariate RR1 (Ref)0.84 (0.46-1.52)0.55 (0.32-0.93)0.46 (0.27-0.77)0.44 (0.26-0.76)<.01
 ≥65      
  No. of cases1212242846 
  Age-adjusted RR1 (Ref)1.42 (0.64-3.17)1.15 (0.58-2.31)1.01 (0.51-1.99)1.25 (0.66-2.36).83
  Multivariate RR1 (Ref)1.51 (0.63-3.62)1.32 (0.61-2.83)0.92 (0.42-2.04)1.32 (0.60-2.89).99
Age at prostate cancer diagnosis, y
 <65      
  No. of cases1513253650 
  Age-adjusted RR1 (Ref)0.90 (0.43-1.88)0.56 (0.30-1.07)0.60 (0.33-1.09)0.62 (0.35-1.11).55
  Multivariate RR1 (Ref)0.78 (0.35-1.73)0.42 (0.21-0.87)0.40 (0.20-0.82)0.43 (0.21-0.88).09
 ≥65      
  No. of cases2522485681 
  Age-adjusted RR1 (Ref)1.22 (0.69-2.17)0.97 (0.60-1.58)0.82 (0.51-1.32)0.92 (0.58-1.44).31
  Multivariate RR1 (Ref)1.19 (0.64-2.18)0.97 (0.57-1.66)0.70 (0.40-1.21)0.78 (0.44-1.36).10
BMI at baseline      
 <25 kg/m2      
  No. of cases137272828 
  Age-adjusted RR1 (Ref)0.89 (0.35-2.23)0.97 (0.50-1.88)0.61 (0.31-1.17)0.54 (0.28-1.04).01
  Multivariate RR1 (Ref)0.69 (0.25-1.89)0.76 (0.35-1.66)0.41 (0.18-0.93)0.43 (0.18-1.00).02
 ≥25 kg/m2      
  No. of cases2626426199 
  Age-adjusted RR1 (Ref)1.16 (0.67-1.99)0.68 (0.42-1.12)0.77 (0.48-1.22)0.89 (0.58-1.37).84
  Multivariate RR1 (Ref)1.07 (0.60-1.91)0.60 (0.35-1.04)0.58 (0.34-0.98)0.63 (0.37-1.08).10

We also conducted analyses stratified according to whether men had or had not received a PSA blood test in the past 3 years. However, we produced no evidence that RRs for moderate/vigorous intensity, light intensity, and total activity differed according to PSA screening (all Pinteraction>.05).

DISCUSSION

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Conflict of Interest Disclosures
  7. References

In this large prospective cohort study of men ages 51 years to 72 years at study baseline, we examined physical activity, according to age period and intensity of activity, in relation to prostate cancer among US whites and US blacks. Similar to previous studies,3 we observed little evidence of a relation between physical activity and prostate cancer among white men. However, among black men, we observed that frequent physical activity of moderate to vigorous intensity during young adulthood (ie, ages 19 years to 29 years) was related to a statistically significant 35% reduction in prostate cancer risk. This relation was particularly pronounced among black men aged <65 years and/or who were light in weight at baseline. A suggestive association also was observed for physical activity of a moderate/vigorous intensity during ages 35 years to 39 years, but the trend did not reach statistical significance. These results provide some evidence that physical activity, particularly during young adulthood, may reduce the risk of prostate cancer among black men. However, because our findings were novel and physical activity was linked only moderately to a reduced risk, these findings require confirmation in future studies.

Contrary to what we expected, frequent activity of a moderate/vigorous intensity during the last 10 years was related to a modestly increased prostate cancer risk among black men. The 95% CIs for each physical activity category were quite wide, suggesting a possible chance finding. To the best of our knowledge, there is no prior biologic rationale for such an association; therefore, further data are required to interpret this finding.

Although they are speculative, there are several potential biologic reasons why physical activity may reduce prostate cancer risk among black men but not among white men. It is known that genetic variants that predispose to prostate cancer are as much as 20 times more common among black men than among white men,16 suggesting different underlying biologic susceptibilities to this disease. It also has been determined that the microenvironment of prostate tumors differs between black men and white men, with higher expression of genes related to inflammation and immune function among prostate tumors in black men.17 Because physical activity reduces inflammation and improves immune function,3 exercise arguably may reduce prostate cancer risk more among black men than among white men. It has been reported that black men have higher levels of testosterone during young adulthood than white men.18 Physical activity increases levels of the binding hormone for testosterone, SHBG,1 and, thus, could be of particular importance among black men for modulating free testosterone levels. It is has been established that resting energy expenditure is lower among blacks by approximately 50 kcal to 160 kcal compared with whites, even after adjusting for body size differences.19 Regular physical activity may help to offset this racial/ethnic difference in energy balance. The roles of inflammation,20 sex steroid levels,2 and energy balance21 in prostate carcinogenesis currently are under investigation; therefore, it is difficult at this time to evaluate the relative importance of each mechanism.

To our knowledge to date, physical activity has been examined in relation to prostate cancer among black men in only 3 previous studies.4-6 Of these studies, 1 study reported that physical inactivity was associated with a 3-fold risk of prostate cancer,4 but the other studies reported null results.5, 6 These studies did not examine physical activity during young adulthood, they also included few cases (in the smallest study, only 47 cases were identified), and they did not examine the same types and intensities of physical activity. These differences prevent any clear conclusions regarding the association between physical activity and prostate cancer among black men.

Young adulthood may be a period of particular interest with respect to prostate cancer risk, because prostate cancer precursors (ie, prostatic intraepithelial neoplasias) often develop early in life, including during young adulthood.22 To the best of our knowledge, the relation between physical activity during young adulthood and prostate cancer has been examined previously in only 2 case-control studies,7, 8 and neither study established a link between physical activity during young adulthood and prostate cancer. Three additional studies examined physical activity over the lifespan, albeit at older ages.9-11 In 2 prospective studies, recreational activity at neither age 30 years10 nor age 40 years11 was linked with prostate cancer risk. In a case-control study, occupational activity, but not leisure activity, during ages 30 years to 39 years was associated with reduced prostate cancer risk.9

Among black men, the reduction in prostate cancer risk conferred by physical activity during young adulthood was especially robust among men who were aged ≤65 years at baseline. This may reflect that prostate cancers diagnosed at a young age may be of different subtypes than prostate cancers diagnosed later in life.23 In the alternative, differing associations by age may be caused by birth-cohort effects. The younger men in our study were born between 1931 and 1945, which coincides with the period of the Great Depression and World War II. These men most likely would have had highly restricted diets during childhood, and this restriction may act in combination with physical activity during young adulthood to reduce prostate cancer risk.

Our study includes several limitations that argue for caution in interpreting the results reported herein. Our assessment of physical activity was based on self-report. The assessment of physical activity during young adulthood, thus, required participants to recall activity from a period 20 to 30 years in the past. Such distant recall may have resulted in imprecise assessment and some error in the estimation of RRs. In previous research, physical activity recalled 15 years into the past was correlated at the level of r = 0.30 with physical activity measured objectively at that time.24 We are not aware of data indicating the validity of physical activity recalled over periods >15 years. The proportion of men in our study who were black (2.2%) was relatively low compared with the proportion in the general population in this age range (approximately 7%-8%).15 This may be due, at least in part, to the tendency of our cohort to attract men of a relatively high education level. Because of disparities in education, there are fewer black men proportionately to recruit at these higher education levels. Although our study included many cases among black men, we did not have sufficient case numbers to examine advanced or fatal prostate cancers. In a previous study within our cohort, physical activity was related similarly to total prostate cancer, advanced prostate cancer, and fatal prostate cancer.25 Although we adjusted for many potential confounding variables, unknown factors associated with both physical activity and prostate cancer may partly explain the associations observed. Given the modest association between physical activity and prostate cancer, our results may have been caused by chance and will need to be confirmed in additional studies.

The strengths of the current study include the prospective design; the large number of prostate cancer cases, which allowed us to analyze white men and black men separately; and the data collected on intensity and frequency of physical activity across the entire lifespan. In addition, extensive data on possible confounding factors were collected from our participants. This allowed us to carefully control for many important lifestyle factors, such as diet, body weight, and supplement use, that are correlated with physical activity.

In conclusion, the results of the current study demonstrated a relation between frequent physical activity of a moderate to vigorous intensity during young adulthood and a reduction in the subsequent risk of prostate cancer among black men. Additional research is needed to confirm our findings and to elaborate further on the potential mechanisms responsible for this association.

Conflict of Interest Disclosures

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Conflict of Interest Disclosures
  7. References

Supported by the Intramural Research Program of the National Institutes of Health, National Cancer Institute, and by grant TU2CA105666 (to S.C.M.).

References

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. Conflict of Interest Disclosures
  7. References
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