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Low vitamin D levels are associated with an increased risk of diabetes in older adults
Last reviewed: 02.07.2025
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A recent systematic review and meta-analysis published in the journal Nutrients by researchers in Italy updated the systematic review and meta-analysis to examine whether low serum vitamin D levels (25-hydroxyvitamin D or 25OHD) could predict 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.
According to the International Diabetes Federation (IDF) Diabetes Atlas, the global prevalence of diabetes among people aged 20–79 years was 536.6 million in 2021 and is projected to increase to 783.2 million by 2045. 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 mellitus, which may be due to its role in pancreaticinsulin secretion, metabolic syndrome, inflammation, and genetic factors. While observational studies and meta-analyses suggest an inverse association between 25OHD levels and diabetes risk, intervention studies provide conflicting results. Some meta-analyses suggest that vitamin D supplementation reduces the risk of diabetes, especially in normal-weight individuals. However, these studies mainly focus on young adults, with limited studies in older adults despite their higher risk for both conditions. Therefore, the researchers in the current study updated a previous systematic review and meta-analysis to investigate whether low serum 25OHD levels (hypovitaminosis D) can predict the onset of type 2 diabetes mellitus in older adults.
In the present study, PubMed and SCOPUS databases were searched to include longitudinal, prospective studies with self-reported diabetes diagnoses, medical records, or American Diabetes Association diagnostic criteria. Cross-sectional studies, studies using non-serum 25OHD estimates, and studies with only subclinical diabetes assessments were excluded. The updated review and meta-analysis included 12 studies, comprising a total of 40,664 older adults from European and North American populations. The mean age of participants was 69.1 years, and 66% were women. The mean follow-up period was 7.3 years.
According to the study, vitamin D influences the risk of type 2 diabetes through several mechanisms, including modulation of insulin secretion and action, reduction of insulin resistance, regulation of calcium and magnesium metabolism, reduction of chronic inflammation, and possible effects on adipose tissue metabolism. Understanding these mechanisms is important to clarify the complex relationships between vitamin D status and metabolic health, particularly 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 outcome heterogeneity. However, the study is limited by its observational design, lack of causal inference, lack of focus on a very old population, lack of gender-specific studies, and the use of 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 in older adults and the focus of existing clinical trials on younger populations, further well-designed studies are needed to confirm these findings in very old populations.