Low vitamin D levels linked to increased risk of diabetes in older adults

A recent systematic study and meta-analysis published in the journal Nutrients by researchers in Italy updated the systematic review and meta-analysis to examine whether low levels of vitamin Din serum (25-hydroxyvitamin D or 25OHD) predicts the onset of type 2 diabetes (T2D) in older adults. Despite adjusting for several potential confounders, low 25OHD levels were found to be associated with an increased risk of developing type 2 diabetes in older adults.

The global prevalence of diabetes among people aged 20–79 years was 536.6 million in 2021 and is projected to rise to 783.2 million by 2045, according to the International Diabetes Federation (IDF) Diabetes Atlas. The prevalence of diabetes is highest among older adults, especially those aged 75–79 years, which will lead to a significant increase in healthcare costs in the near future.

Vitamin D deficiency, common among older adults, is associated with an increased risk of type 2 diabetes, which may be due to its role in the secretion of insulin pancreas, metabolic syndrome, inflammation and genetic factors. While observational studies and meta-analyses indicate an inverse association between 25OHD levels and diabetes risk, intervention studies provide conflicting results. Some meta-analyses show that taking vitamin D reduces the risk of diabetes, especially in people with normal body weight. However, these studies mainly focus on younger adults, with limited research on older adults despite their higher risk for both conditions. Therefore, the researchers in the present study updated a previous systematic review and meta-analysis to examine whether low serum 25OHD levels (hypovitaminosis D) can predict the onset of type 2 diabetes in older adults.

The present study searched the PubMed and SCOPUS databases to include longitudinal, prospective studies with diabetes self-diagnosis, medical records, or American Diabetes Association diagnostic criteria. Cross-sectional studies, studies using non-serum 25OHD assessments, and studies with only subclinical diabetes assessments were excluded. The updated review and meta-analysis included 12 studies covering a total of 40,664 older adults from European and North American populations. The average age of participants was 69.1 years, and 66% were women. The average follow-up period was 7.3 years.

Vitamin D affects the risk of type 2 diabetes through several mechanisms, including modulating insulin secretion and action, reducing insulin resistance, regulating calcium and magnesium metabolism, according to research. Reduction of chronic inflammation and possible effects on adipose tissue metabolism. Understanding these mechanisms is important for elucidating the complex relationships between vitamin D status and metabolic health, especially in the context of diabetes prevention and management.

The study is unique in that it examines the association between vitamin D and incident type 2 diabetes in older adults with a large sample size, extensive adjustment for covariates, and a long follow-up period with low heterogeneity in outcomes. However, the study is limited by its observational design, lack of causal inferences, lack of focus on a very elderly population, lack of gender-specific studies, and use of a radioimmunoassay to measure serum 25OHD levels, which may be less accurate than the chemiluminescence method.

In conclusion, the present meta-analysis shows that low vitamin D levels are associated with an increased risk of diabetes in older adults, even after adjusting for various potential confounders. This confirms and updates the findings of the 2017 study. The results highlight the broader impact of vitamin D beyond bone health. Given the prevalence of vitamin D deficiency among older adults and the focus of existing clinical trials on younger populations, further well-designed studies are needed to confirm these findings in very elderly populations.