The results, published in Lancet Diabetes & Endocrinology, found no causal link between a person's vitamin D levels and whether they developed type-2 diabetes when the genes that controlled blood levels of the vitamin were examined.
These latest results, drawing on data from 35 studies, challenged previous observational studies that suggested the development of the disease was associated with vitamin D deficiency.
Dr Nita Forouhi, one of the researchers behind the study, said: "Our findings suggest that interventions to reduce the risk of type-2 diabetes by increasing concentrations of vitamin D are not currently justified.
“Observational studies that show a strong and consistent higher risk of type-2 diabetes with lower levels of vitamin D may do so because they have thus far not been able to adequately control for distorting or confounding factors, such as physical activity levels, that may be related both to vitamin D levels and to the risk of type-2 diabetes."
New findings questioning the old
The meta-analysis of 35 short-term trials, which included populations of European descent with and without type 2 diabetes, looked at the single nucleotide polymorphism DNA sequence within or near four genes relevant to vitamin D synthesis and metabolism: DHCR7, CYP2R1, DBP (also known as GC) and CYP24A1.
They assessed these single nucleotide polymorphisms (SNPs) for associations with circulating vitamin D concentrations (5449 non-T2 cases from two studies), the risk of T2 diabetes (28,144 T2 cases, 76 344 non-T2 cases from five studies) and glycaemic traits (46,368 non-T2 cases from a study consortium).
This was then compared to a meta-analysis of data from observational studies (8492 T2 cases, 89,698 non-T2 cases from 22 studies) that looked at the association between vitamin D concentrations and T2 diabetes.
The results showed that all four genes were associated with vitamin D concentrations in the body. However, the researchers concluded that an association with the disease was, “unlikely to be causal”.
‘We are far from done with this topic’
Dr Forouhi said that while these findings did not provide sufficient support for this causal role, “we are far from done with this topic”.
She that further research was needed with better clinical trials and observational studies with more precise measurement of important factors that may affect the relationship.
"Until then, we need to be cautious about vitamin D's potential role in the prevention of type 2 diabetes and stick to things that are proven to work – diet and exercise," she said.
Source: The Lancet Diabetes & Endocrinology
Published online ahead of print, doi:10.1016/S2213-8587(14)70184-6
'Association between circulating 25-hydroxyvitamin D and incident type 2 diabetes: A mendelian randomisation study'
Authors: Z. Ye, S. J. Sharp, S. Burgess, R. A. Scott, F. Imamura, C. Langenberg, N. J. Wareham, N. G. Forouhi