Systematic review finds that vitamin D intake in early life may be associated with a reduced risk of type 1 diabetes

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Vitamin D is suspected of having a role in the development of type 1 diabetes.  Previous studies have been small-scale and inconclusive.

Now we have a systematic review of the observational evidence about the relationship between consumption of Vitamin D in early life (or during pregnancy) and the risk of developing type 1 diabetes later on in life.

Methods

The review team searched PubMed, Web of Science and the Cochrane Library.  They extracted data from these studies about vitamin D intake, rates of type 1 diabetes and any statistical adjustments made by the researchers.

The data were analysed using a random effects model.  Further analyses were planned to investigate the effects of study design on outcomes.

Results

They found 11 relevant studies which spanned between 5 and 30 years of follow-up.  8 of these studies looked at Vitamin D intake during early life and 3 looked at maternal Vitamin D intake during pregnancy.

When the reviewers pooled the data from these studies, they found a statistically significant association between Vitamin D intake  in early life and a reduced risk of developing type 1 diabetes later on, with an odds ratio of 0.71 (95% CI, 0.51–0.98).

There was no evidence of benefit for maternal supplements.

Since this type of research can only establish an association, not causation, further prospective studies are warranted to confirm the link.

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Some of the studies used supplements whilst others used diet questionnaires to establish vitamin D intake.

Comments

  • This observational evidence does not prove causation.  It may be that taking vitamin D supplements is just acting as a marker of other health-conscious behaviour.
  • The reviewers did not search EMBASE.  It may be that there is other important evidence that can add to this picture.
  • The reviewers did not carry out an explicit assessment of the quality of the studies, although the characteristics of each are described.  It seems that there is some risk of bias in these studies, such as due to small sample size and event rates.
  • Subgroup and sensitivity analyses did not clarify things any further, largely due to small event rates in the cohort studies.
  • They did do an analysis of heterogeneity, and found that there were important differences between the studies, in terms of the way they measured exposure to vitamin D, adjusted outcomes for other factors and in the results themselves.
  • It should also be noted that the confidence interval is rather wide, and close to the point of no difference.  Therefore, data from future research might alter the conclusion.

Reference

The full text is available for free from the journal Nutrients: