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Keywords:

  • blood viscosity;
  • high water intake;
  • infarction;
  • quality of life;
  • urinary frequency

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Subjects and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Abstract:  Physicians recommend a high water intake to prevent cerebral infarction by decreasing blood viscosity. However, there is no evidence that high water intake decreases viscosity, although it increases urinary frequency. Therefore, we investigated the change of blood viscosity and urinary frequency by high water intake. We examined the change of blood viscosity after acute water intake, the circadian rhythm of blood viscosity, and the change of early morning blood viscosity and urinary frequency after high water intake for 1 week in healthy volunteers aged 31–75 years. Blood viscosity decreased transiently by acute water intake, but remained within the range of its circadian rhythm. Morning blood viscosity did not alter by high water intake for 1 week, although urinary frequency increased. Because excessive water intake increases urinary frequency without decreasing blood viscosity, a high water intake should not be recommended in persons with urinary frequency.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Subjects and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Recently, many physicians and neurologists in Japan have recommended a high water intake (>2 L per day) to prevent cerebral infarction or myocardial infarction by decreasing blood viscosity, because increased blood viscosity is positively correlated with the occurrence of stroke or myocardial infarction.1,2 However, there is no definite evidence that stroke or myocardial infarction can be prevented by high water intake, and that increasing the intake of water can actually decrease the blood viscosity. While, excessive intake of water could possibly increase the number of patients consulting urologists because of urinary frequency or nocturnal urinary frequency (nocturia). In particular, nocturia is a common symptom in the elderly, and it has a major adverse impact on the quality of life.3 Nevertheless, many of patients with nocturia are drinking a large volume of water to prevent cerebral infarction or myocardial infarction in accordance with the recommendation of their physician or neurologist. Because increased blood viscosity is suggested to cause a decrease of blood fluidity that leads to venous stasis,4 it is easy to understand that the risk of cerebral infarction or myocardial infarction may be increased by dehydration. However, it is doubtful whether a high water intake is useful for preventing stroke or myocardial infarction in elderly persons who are not dehydrated. In the present study, we investigated the change of blood viscosity and urinary frequency in subjects with a high water intake.

Subjects and methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Subjects and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

We performed three studies to investigate the effect of a high water intake on blood viscosity and urinary frequency in healthy volunteers. All subjects were hospital staff (doctors, nurses and paramedics) or their family members, and all of them had a good performance status. They were working or resting in a comfortable temperature environment all day. There were no subjects with evidence of psychiatric disorders, cerebrovascular disease, neurological disease, cardiorespiratory disease, renal or liver disease, or diabetes mellitus, and none of them were taking any medicines.

Study 1

Six volunteers (two men and four women, aged 31–51 years) were enrolled in this study. Each subject urinated and provided a blood sample in the fasting state. Then 1 L of tap water was ingested within 5 min, and further blood samples were collected at 1 and 2 h after water intake in order to assess the change of blood viscosity caused by an acute water load. Each blood sample (20 mL) was immediately added to by heparin sodium (100 U/0.1 mL), and was kept at the room temperature for approximately 1 h. Blood viscosity and urinary frequency before and after water intake were compared in each subject. Blood viscosity was determined by using a Sine-wave Vibro Viscometer (A&D, Tokyo, Japan), which measures viscosity by detecting the electrical current necessary to vibrate two sensor plates at a constant frequency of 30 Hz and an amplitude of less than 1 mm at 28°C.

Study 2

Six volunteers (three men and three women, aged 31–53 years) were enrolled. A fasting blood sample was collected at 6:00 am (before breakfast) from each subject, and additional blood samples were collected at every 4 h until 10:00 pm and also at 6:00 am the next morning. During this experiment, there were no restrictions on food and fluid intake. The viscosity of each blood sample was measured to determine the circadian rhythm of blood viscosity.

Study 3

Twenty-one volunteers (20 men and one woman, aged 31–75 years) were enrolled. There were 10 persons under 65 years old with a low mean frequency of nocturnal urination (an average of <1 time from the start of sleeping until the next morning), and 11 persons over 65 years old with a higher mean frequency of nocturnal urination (an average >1 time). A fasting blood sample was collected at 6:00–7:00 am (before breakfast) from each subject, and they all drank at least 2 L of tap water every day for 1 week. Another fasting blood sample was collected at 6:00–7:00 am (before breakfast) after 1 week in order to examine the change of early morning blood viscosity due to a high water intake. The mean daytime and nighttime urinary frequency was assessed for 3 days before and after this 1-week period of high water intake.

Results are reported as the mean ± standard deviation. A Student's t-test for paired data was used for statistical analysis, and P < 0.05 was considered to indicate statistical significance.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Subjects and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

In study 1, blood viscosity was 5.47 ± 0.66 mP/s before drinking 1 L of water, and it decreased by 3.8% at 1 h after water intake (5.26 ± 0.68 mP/s) and by 6.0% at 2 h afterward (5.13 ± 0.54 mP/s) (Fig. 1). The minimum blood viscosity was recorded at 1 h after water intake in two women, and at 2 h after water intake in the remaining two men and two women. From the start of observation until 2 h after water intake, the subject passed urine an average of 3.0 times.

image

Figure 1. Change of blood viscosity after acute water intake. Blood viscosity decreased at 1 h and 2 h after intake of 1 L of water.

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In study 2, although three of the six volunteers showed their maximum blood viscosity at 6:00 am, the timing of the maximum or minimum blood viscosity differed between individuals. The largest (5.79 mP/s at 6:00 am and 5.29 mP/s at 10:00 pm) and smallest differences (4.64 mP/s at 6:00 am and 4.43 mP/s at 6:00 pm) between the maximum blood viscosity and the minimum viscosity were 10.7% and 4.5%, respectively. The average difference between the maximum blood viscosity (5.18 ± 0.76 mP/s) and the minimum viscosity (4.93 ± 0.67 mP/s) was 4.8% (Fig. 2).

image

Figure 2. Circadian rhythm of blood viscosity under normal conditions. The time of the maximum or minimum blood viscosity differed between the subjects. The average difference between the maximum and minimum blood viscosity values was 4.8%.

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In study 3, early morning blood viscosity did not alter by a high intake of water for 1 week (5.56 ± 0.43 mP/s) when compared with the baseline value (5.61 ± 0.44 mP/s) (Fig. 3), but the mean urinary frequency showed a significant increase during both the daytime and nighttime (Table 1). We also divided the subjects into two groups according to their age (under 65 years old vs over 65 years old), and then compared the change of blood viscosity and urinary frequency. In 10 subjects under 65 years old, early morning blood viscosity did not alter by a high intake of water for 1 week (5.64 ± 0.47 mP/s) compared with the baseline value (5.76 ± 0.47 mP/s), but the mean urinary frequency during daytime significantly increased. In 11 elderly subjects over 65 years old, early morning blood viscosity did not alter by a high intake of water for 1 week (5.49 ± 0.47 mP/s) compared with the baseline value (5.47 ± 0.39 mP/s), but the mean urinary frequency significantly increased during both the daytime and nighttime (Table 1).

image

Figure 3. Early morning blood viscosity before and after a high intake of water (at least 2 L of water daily) for 1 week. Data were obtained from 21 healthy volunteers (including 11 elderly persons over 65 years old). Early morning viscosity did not alter by increasing the water intake for 1 week.

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Table 1.  Mean urinary frequency before and after drinking at least 2 L of water daily for 1 week
SubjectsDaytime (times) Nighttime (times) 
  1. Mean ± SD.

All 21 persons
 Before7.4 ± 2.4P < 0.0010.9 ± 1.1P = 0.002
 After 1 week10.3 ± 2.9 1.7 ± 1.5 
10 persons <65 years old
 Before7.0 ± 3.0P = 0.0420.4 ± 0.9 
 After 1 week9.3 ± 2.6 0.7 ± 0.9 
11 persons >65 years old
 Before7.8 ± 1.8P = 0.0031.3 ± 1.1P = 0.005
 After 1 week11.2 ± 3.0 2.6 ± 1.2 

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Subjects and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

It has been reported that blood viscosity is increased in patients with ischemic heart disease or cerebrovascular disease, and that dehydration may be one of the causes of myocardial ischemia or stroke.1,2 Blood viscosity increases during hot and dry weather,5 and bathing in hot-springs may cause a transient change of blood viscosity that induces acute cerebral infarction or myocardial infarction.6 It has also been reported that the infarct rate is higher in the early morning because blood viscosity increases at this time.7 Based on such findings, many physicians and neurologist (as well as the mass media) have recommended a high water intake as a useful precaution. However, there is no definite evidence that stroke or myocardial infarction can be prevented by increasing the water intake in daily life, and that a high intake of water will actually decrease blood viscosity. Even in patients with acute ischemic stroke, there is no strong evidence that hemodilution therapy or heparin-induced extracorporeal low-density lipoprotein precipitation has a beneficial effect.8 On the other hand, excessive intake of water could increase the number of patients who consult urologists because of urinary frequency or nocturia. Indeed, many patients with nocturia are found to be drinking an excessive water load to prevent stroke or myocardial infarction, even though they are not dehydrated.

Drinking liquids that contain electrolytes late at night has been reported to decrease the blood viscosity on the next morning.9 However, there is also a possibility that such fluids will be stored in the extracellular compartment, placing a burden on the heart and increasing the blood pressure. Water that accumulates in the extracellular space during the daytime may enter the intravascular compartment and increase the circulating blood volume, thus bringing about an increase of natriuretic peptide that increases urine production. It was also reported that drinking six mugs of tea daily did not affect the plasma levels of fibrinogen, tissue-type plasminogen activator, and plasminogen activator inhibitor-1, which are factors related to blood viscosity.10 The present study revealed a transient decline of blood viscosity after acute water intake, but it remained within the circadian range of viscosity values. In addition, high water intake for 1 week did not decrease the blood viscosity in the early morning (the time when cerebral infarction is most likely to occur), but the mean urinary frequency significantly increased. These results clearly show that an excessive water load is excreted as urine without decreasing blood viscosity. Especially in our elderly subjects (>65 years old), a high water intake caused a significant increase of urinary frequency of nighttime (nocturia), as well as daytime.

Nocturia can have a major impact on the quality of life in elderly persons. Therefore, a high water intake should not be recommended without good reason in person who has urinary frequency, especially elderly persons who are troubled by nocturia.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Subjects and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

This study was supported by a Research Grant (H16-Choju-008) for Comprehensive Research on Aging and Health from the Japanese Ministry of Health, Labour and Welfare, and a 2005 Grant from Mitsui Sumitomo Insurance Welfare Foundation of Japan.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Subjects and methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  • 1
    Lowe GD, Lee AJ, Rumley A et al. Blood viscosity and risk of cardiovascular events: the Edinburgh Artery Study. Br. J. Haematol. 1997; 96: 16873.
  • 2
    Kowal P. Hemorheology in cerebral ischemia. Neurol. Neurochir. Pol. 1996; 30: 711.
  • 3
    Blanker MH, Bernsen RM, Bosch JL et al. Relation between nocturnal voiding frequency and nocturnal urine production in older men: a population-based study. Urology 2002; 60: 61216.
  • 4
    Mchedlishvili G. Disturbed blood flow structuring as critical factor of hemorheological disorders in microcirculation. Clin. Hemorheol. Microcirc. 1998; 19: 31525.
  • 5
    Kolar J, Bhatnagar SK, Hudak A et al. The effect of a hot dry climate on the haemorrheology of healthy males and patients with acute myocardial infarction. J. Trop. Med. Hyg. 1988; 91: 7782.
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    Kubota K, Tamura K, Take H et al. Acute myocardial infarction and cerebral infarction at Kusatsu-spa. Nippon Ronen Igakkai Zasshi 1997; 34: 239.
  • 7
    Nadav L, Gur AY, Korczyn AD et al. Stroke in hospitalized patients: are there special risk factors? Cerebrovasc. Dis. 2002; 13: 12731.
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    Lechner H, Walzl M, Walzl B et al. First experience in application of heparin-induced extracorporeal LDL precipitation (HELP) in acute thromboembolic stroke. Ital. J. Neurol. Sci. 1993; 14: 2515.
  • 9
    Kurabayashi H, Kubota K, Tamura J et al. A glass of water at midnight for possible prevention of cerebral infarction. Stroke 1991; 22: 13267.
  • 10
    Vorster H, Jerling J, Oosthuizen W et al. Tea drinking and haemostasis: a randomized, placebo-controlled, crossover study in free-living subjects. Haemostasis 1996; 26: 5864.