Does Vitamin D Have a Role in Diabetes?

Associations between Vitamin D Levels and Insulin Resistance in Non-Diabetic Obesity: Results from NHANES 2001-2018

OBJECTIVE

Obesity is often accompanied by insulin resistance (IR) and diabetes. We explored the association between vitamin D levels and IR in non-diabetic obesity.

METHODS

We conducted a cross-sectional study based on the data of National Health and Nutrition Examination Survey (NHANES) from 2001 to 2018. Non-diabetic individuals (aged ≥20 years) with obesity (BMI ≥ 30kg/m2) were included in the study. And HOMA-IR ≥ 2.5 was defined as IR. The multivariable linear regression models were constructed to evaluate the associations between levels of 25(OH)D and HOMA-IR. We calculated the odds ratio (OR) and 95% confidential intervals (CIs) for associations between 25(OH)D deficiency and IR in obesity using multivariable logistic regression models.

RESULTS

Overall, a total of 3887 individuals were included in this study. Serum vitamin D level was significant lower in obesity participants with IR than that of non-IRs. The linear regression models showed that vitamin D level was inversely associated with HOMA-IR in obesity after adjusting for covariables (β=-0.15, 95%CI (-0.28, -0.02), p = 0.028). And the multivariable logistic regression models indicated an association between vitamin D deficiency and IR in obesity ((OR= 1.38, 95%CI (1.09-1.73), p = 0.007)). The further stratified regression analyses among different BMI demonstrated that vitamin D deficiency (OR = 1.4, 95%CI (1.05,1.86), p = 0.022) only contributed to developing IR in class I obesity.

CONCLUSION

This study suggested an association of vitamin D levels with IR in obesity. And vitamin D deficiency contributed to IR in class I obesity.

The imprecision of micronutrient requirement values: the example of vitamin D

Food, not nutrients, is the fundamental unit in nutrition. Nutrient requirement values and recommended daily intakes have long been determined and organized in tables by several regulators. These figures, however, overlook the complexity of mixing different foods in a diet and the mediation by human gut microbiota on digestion, metabolism, and health. The microbiome molecular mechanisms and its potential influence on nutrient requirements are far from clear. Guidelines should depend on the sort of intake, along with the dietary habits, rather than focusing on single nutrients. Despite many decades of attempts to investigate the proximate nutrient composition of foods consumed by different world populations, there are still neither standardization of food composition databases nor harmonized dietary intake methods of assessment of nutrients. No all-inclusive attempt was yet made to emphasize the requirements of the various micronutrients, phytonutrients, and non-nutrients on gut microbiota and vice versa, and thereafter reflected into dietary guidelines. New multifaceted methods have been advanced to reevaluate the way nutrients and nutrient requirements are assessed within the intricate biological systems. Our main goal here was to enhance the fact that existing food guidelines hold inherent strengths and limitations but fail, in many aspects, namely, in not taking into account essential geographical, ethnic and cultural differences, and the different stages of life, infant nutrition, and the microbiota impact on several micronutrient requirements. Vitamin D is given as an illustration on present inaccuracy of its requirements. Defining dietary reference intakes is therefore an ongoing process specific for each population.

Additive Effects of Exercise and Vitamin D Supplementation (with and without Calcium) on Bone Mineral Density in Older Adults: A Systematic Review and Meta-Analysis

Exercise is a recognized component in the prevention and therapy of osteoporosis. The present systematic review and meta-analysis aimed to determine the effect of Vitamin D (Vit-D) added to exercise versus exercise alone on bone mineral density (BMD) at the lumbar spine (LS) or hip in older adults. A systematic review based on six literature databases according to PRISMA included (a) exercise trials, with an exercise (EX) and a combined exercise + Vit-D group (EX + Vit-D), (b) intervention ≥ 6 months, and (c) BMD assessments at LS or hip. Effects sizes (MD) and 95%-confidence intervals (95%-CI) were calculated using a random-effect model that includes the inverse heterogeneity model (IVhet). Five studies with 281 participants in the EX and 279 participants in the EX + Vit-D were included. No significant differences between EX versus EX + Vit-D were observed for BMD-LS (MD: 0.002, 95%-CI: -0.033 to 0.036) or BMD-hip (MD: 0.003, 95%-CI: -0.035 to 0.042). Heterogeneity between the trial results was moderate-substantial for LS (I2 = 0%) and moderate for hip-BMD (I2 = 35%). The funnel plot analysis suggests evidence for a publication/small study bias for BMD-LS and hip results. In summary, this present systematic review and meta-analysis were unable to determine significant positive interaction of exercise and Vit-D on LS- or hip-BMD. We predominately attribute this finding to (1) the less bone-specific exercise protocols of at least two of the five studies and (2) the inclusion criteria of the studies that did not consequently focus on Vit-D deficiency. This issue should be addressed in more detail by adequately powered exercise trials with promising exercise protocols and participants with Vit-D deficiency. This trial is registered with the International Prospective Register of Systematic Reviews (PROSPERO) ID: CRD42022309813.