Association of dietary calcium, magnesium, and vitamin D with type 2 diabetes among US adults: National health and nutrition examination survey 2007–2014—A cross‐sectional study

Abstract Higher dietary intake of calcium (Ca), magnesium (Mg), and vitamin D has been associated with reduced risk of type 2 diabetes (T2DM), and a higher intracellular ratio of Ca to Mg leads to insulin resistance. Previous epidemiological studies did not examine the combined effects of dietary Ca, Mg, and vitamin D as well as ratio of Ca to Mg with T2DM. Therefore, we assessed the relationship between dietary intakes of Mg, Ca, and vitamin D (using 24‐hr recalls) individually and in composite and T2DM in the National Health and Nutrition Examination Survey 2007–2014, which involved 20,480 adults (9,977 men and 10,503 women) with comprehensive information on related nutrients, and anthropometric, demographic, and biomarker variables using multivariable logistic regression. The results indicated that dietary calcium at Q3 (812 mg/day) was significantly linked with T2DM in women (OR: 1.30; 95% CI: 1.02, 1.65). Dietary vitamin D at Q3 (5.25 μg/day) significantly reduced the odds of T2DM by 21% in men (OR: 0.79; 95% CI: 0.64, 0.98). This is an interesting study that has important implications for dietary recommendations. It is concluded that US adults having dietary Ca below the RDA were associated with increased risk of T2DM in all population and women, while higher ratio of Ca to Mg was associated with increased risk of T2DM in all population and increased vitamin D intake is related to decreased risk of T2DM in men. Moreover, further research is needed to make more definitive nutritional recommendations.


Definition of diabetes according to the American Diabetes
Association (ADA) is a group of metabolic diseases characterized by hyperglycemia resulting in either deficiency of insulin secretion, insulin action, or both (Diabetes Care, 2004). Type 2 diabetes is increasing worldwide; hence, it is a chronic disease (). The prevalence of type 2 diabetes in 2005 was 1 in 10 in every 5 adults, while that was predicted to be 1 in 3 adults by the end of 2050 (Boyle et al., 2010). T2DM is associated with poor nutrient intake (McNaughton SA, Mishra GD, Brunner EJ 2008) especially calcium and vitamin D were considered as "nutrient of concerned" (Dietary Guidelines for American (2010) while magnesium was considered as "shortfall nutrient" (United States Department of Agriculture, 2010).
Dietary factors have a key role in the incidence and development of chronic diseases, especially T2DM (McNaughton et al., 2008).
Moreover, about 40% of American populations did not meet the daily requirements of calcium from their diet (US Department of Agriculture, 2015). Calcium has a vital role in the prevention of diabetes by improving insulin sensitivity and pancreatic β-cell functions (Pittas et al., 2007). Insulin secretion depends on calcium, and thus, alterations in calcium flux adversely affect beta-cell secretion (Pittas et al., 2007).
Also, dietary calcium was inversely associated with T2DM in several epidemiological studies (Pittas et al., 2006;Villegas et al., 2009). However, some studies showed inconclusive results (De Boer et al., 2008;Kirii et al., 2009). Meta-analysis and other research studies conducted on the American populations show a significant inverse association between risk of T2DM and low magnesium intake (Dong et al., 2011;Hruby et al., 2014). Especially, magnesium status is low in populations that eat processed diets; therefore, there is a need to explore the concerns of suboptimal magnesium status because low magnesium was related to the threat of type 2 diabetes (Rosanoff et al., 2016).
Potentially, cellular glucose metabolism is directly regulated through magnesium by affecting rate-limiting enzymes of glycolysis (Musso, 2009). Magnesium significantly reduces the risk by 36% in Japanese men and women when compared to highest (303 mg/day) quartile versus lowest (158 mg/day) quartile . Oral magnesium supplementation of 250 and 365 mg/day for the period of 3 and 6 months decreased insulin resistance in the randomized control trial (RCT; Mooren et al., 2011). A higher intracellular ratio of Ca: Mg leads to insulin resistance and hypertension in the NHANES study (Moore-Schiltz et al., 2015). According to the hypothesis of Roasanoff (2010), low magnesium and high calcium diet may lead to cellular calcium activation from low magnesium levels, and future studies are obligatory to realize the potential effects of the ratio of Ca to Mg (Nielsen, 2010;Rosanoff, 2010). However, foods fortified with vitamin D were the main food for vitamin D intake in the United States (Holick, 2007). Human studies, and animal and human cell experiment show the protective effects of vitamin D and T2DM (Danescu et al., 2009;Kadowaki & Norman, 1984). NHANES data indicated that serum 25-OHD was inversely found to be in doseresponse patterns in non-Hispanic whites and Mexican Americans (Scragg et al., 2004). Vitamin D stimulates the expression of insulin receptor and bindings with the beta-cell receptor, thus affects directly the impaired beta-cell function and insulin resistance and indirectly changeable calcium flux and extracellular calcium through β-cell (Pittas et al., 2007).
Using NHANES (2007NHANES ( -2014, however, no previous epidemiological studies have directly examined the effect of dietary calcium, magnesium, vitamin-D and ratio of Ca:Mg and risk of T2DM, therefore, the purpose of this study was to examine the individually as well combine effect of dietary calcium, magnesium , ratio of calcium to magnesium (Ca:Mg) and vitamin D using their relevant cutoff points (RDA, Quintiles) and T2DM in US adults, the hypothesis shows that dietary calcium, magnesium, and vitamin-D individually and in combination would decrease the risk of T2DM.
Hence, the aim to conduct this study was to examine the potential association of dietary intake for magnesium, calcium separately and in combinations consuming their ratio (Mg:Ca), and vitamin D, with type 2 diabetes among US adults, and the previous hypothesis reported that dietary calcium, magnesium, and vitamin D separately and in grouping would decrease the risk of T2DM.

| Study populations
This Cross sectional Study used NHANES data sets 2007-2014 data, NHANES is US national representative survey managed by center for disease control and prevention (CDC). NHANES is a consecutive survey conducted every two years, representing one cycle of the US civilian noninstitutionalized population, and NHANES data set is publically available at http://www.cdc.gov/nchs/nhanes.htm.

| Ascertainment of T2DM
The respondents diagnosed with T2DM or one of the criteria as recommended by the American Diabetes Association (Classification, 2014) will be counted as cases, having hemoglobin A1C ≥ 6.5% and/ or fasting glucose ≥ 7 mmol/L and/or having diagnosed T2DM.

| Dietary assessment
The multipass approach method was used to measure dietary intake of magnesium, vitamin D, and calcium during in-person 24-hr dietary recall (Moshfegh et al., 2008). This method is a precise and brief list

| Study covariates
Data about sex, age, annual household income, ethnicity, educational level, smoking, and drinking position were in use from NHANES in-person household interviews (Zipf et al., 2013). The covariates are as follows: smoking status (used tobacco/nicotine for the last 5 days), drinking status (had at least 12 alcohol drinks/year), physical activity (yes/no), overweight, and obesity classification (Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, 1998). Also, total energy intakes were divided into 10 groups, while fasting glucose and glycohemoglobin (HbA1c) were used as indicators to define our outcome. Data from NHANES 2007, 2009 and laboratory data for each member were combined using unique participant identifier and took into complex sampling design. The complex and four-stage probability sampling design was used to select participants of each NHANES cycle (NHANES, 2010). Dietary calcium, magnesium, a ratio of Ca:Mg, and vitamin D intakes were adjusted for energy intake (as a continuous variable) by the residual method explained by Willett and Stampfer) (Willett, 1998).

| Statistical analysis
Categorical and constant variables were presented using percentages and mean ± SD, respectively. Logistic regression models were used to examine the association between T2DM and calcium, magnesium, vitamin-D and Ca:Mg intake separately and each nutrient categorized into quintiles with the lowest quintile as reference (models 1-3) and Quintile 4 as reference (model 4-6) by using logistic regression models, p-value .05. Furthermore, we also stratified our models by sex and evaluated the intake of calcium and magnesium based on RDA (further down RDA or meeting the RDA based on sexand age-specific recommendations) for individual nutrient (Institute of Medicine, 2012; Institute of Medicine, 1997).
Model 1 was accustomed to sex, race, and age. Model 2 was moreover adjusted for body mass index groups (kg/m 2 ), educational level, exercise regularly (yes/no), current smoker (yes/no), current drinker (yes/no), annual household income, energy intake in groups, total vitamin D (mg/day) (for the model including calcium, magnesium quintile, Ca:Mg ratio quintile), or total Ca:Mg ratio intake (mg/ day) (for the model including vitamin D quintile). Model 3 was further additionally adjusted for total calcium (mg/day) (model including magnesium quintile), total calcium (mg/day) (model including magnesium quintile).

| RE SULTS
The study included 20,480 adults, using data from NHANES 2007-2014, which included cases (T2DM, n = 3,432) and noncases (nondiabetes, n = 17,048) ( Table 1). The occurrence of type 2 diabetes in F I G U R E 1 Study flowchart on selection of the participant TA B L E 1 Selected characteristics of participants according to type 2 diabetes status in the National Health and Nutrition Examination Survey (NHANES, 2007(NHANES, -2014
The culprit mechanism in our study for such observed association) as vitamin-D facilities intestinal calcium absorption and insufficient calcium (due to vitamin-D insufficiency, low calcium intake) because calcium is required in regulating glucose intolerance due to vitamin-D deficiency in vivo (Beaulieu et al., 1993).
The results of the meta-analysis show 600 mg/day calcium intake as desirable, while 1,200 mg daily intake was considered to be preferred (Pittas et al., 2006). Some studies showed a nonsignificant association between dietary magnesium and diabetes (Hopping et al., 2010;Wang et al., 2005). Likewise, the intake of magnesium in our study was low as the intake in the national sample of African American women (median: 183 mg/day) that is below the RDA (320 mg/day) (Ford & Mokdad, 2003). Also, in Mg and glucose metabolism the results are inconsistent (De Valk, 1999 (Kao et al., 1999).
Our results had a significant association among race (p trend = .013), while one of the studies reported ethnic differences to exist among NHANES participants (Scragg et al., 2004). Also, a nonsignificant association between dietary magnesium and diabetes, OR: 0.73; 95% CI: 0.51, 1.04, conclusions from the Melbourne collaborative cohort study (Hodge et al., 2004;Li et al., 2009), supports our findings. The results of our study are generally consistent with previous cross-sectional studies conducted on non-Hispanic whites and Mexican Americans aged ≥ 20 years and found an inverse relationship between vitamin D and diabetes (Scragg et al., 2004 (Pittas et al., 2006). The result of our study matched with finding RR; 0.87;95% CI; 0.75-1.00 when the model were adjusted for several factors including dietary magnesium, retinol, and calcium, a non-significant association was observed between vitamin-D3 intake and T2DM (Pittas et al., 2006), while similar findings from another nested case-control study (Robinson et al., 2011). The findings of our study showed that 60% of participants were non-Hispanic white and few participants fall in our highest quintile (Q5). Conversely, overweight is still a well-known risk factor for T2DM in many studies (Colditz et al., 1995). The results of other studies indicated that genetic variants of dietary magnesium channels such as TRPM6 and TRPM7 increased the incidence risk of T2DM when the dietary intake for magnesium is less than 250 mg/day (Song et al., 2009). Higher calcium-to-magnesium ratio leads to inappropriate cellular calcium activation, which leads to T2DM, CVD, and other diseases if the magnesium deficiency is not corrected (Rosanoff, 2010). In this study, first time we evaluated the individual and combined effects of magnesium, calcium, vitamin D, and Ca: Mg ratio using 8 years of NHANES data, which are the US nationally large representative sample, which demonstrates the strength of this study; secondly, adjustment for several confounding factors; thirdly, the trained staff with standardized protocols of NHANES and efficacy and precision of the data; and fourthly, the criteria been used for case ascertainment ensured all cases were included in the study.
However, processed foods, soda/ soft drinks, beverages, poor nutrient choices, and unhealthy diet will not able the American to meet the daily recommended intake of these micronutrients and health professionals need strategies and dietary interventions, which are an important aspect of epidemiology and public health (O'Neil et al., 2012). chronic ailments of global concern include T2D as their public health importance.

| CON CLUS IONS
This is an interesting study that has important implications for dietary recommendations. It is concluded that dietary calcium intake level of 812 mg/day (Q3) will raise the threat of developing T2DM in the general population and women. Additionally, the findings conclude that US adults having dietary calcium below the RDA were related to an enhanced risk of T2DM in all population, while higher ratio of Ca to Mg was associated with increased risk of T2DM in all population and increased vitamin D intake was associated with decreased risk of T2DM in men. Therefore, the conclusions should probably call for further studies to confirm these results in other settings.