Does Early Vitamin D Supplementation Prevent Type 1 Diabetes?

Vitamin D supplementation has been associated with protection against development of type 1 diabetes mellitus. U.K. investigators conducted a systematic review and meta-analysis (based on 1 cohort study and 4 case-control studies involving 1429 cases and 5026 healthy controls) in which they compared risk for type 1 diabetes among people who did or did not receive supplemental vitamin D during infancy. The methodologic quality of all five of these European retrospective studies was rated as moderate.

In the meta-analysis, infants who received vitamin D supplementation were significantly less likely than those who did not receive it to have developed diabetes by 15 to 30 years of age (odds ratio, 0.71). When cod liver oil was the source of vitamin D, more-frequent supplementation was related to lower risk (OR, 0.81 for 1–4 times weekly; OR, 0.74 for ≥5 times weekly). Frequency of other types of vitamin D supplementation had a negligible effect on risk. In the cohort study, regular doses of vitamin D (2000 IU) were associated with significantly lower risk for diabetes than were smaller doses (OR, 0.22). In one study, in which timing of supplementation was evaluated, infants who began supplementation between ages 7 and 12 months had lower risk for diabetes later in life than those who began supplementation before age 6 months. Finally, in one study, duration of supplementation for less than or more than 1 year lowered risk by similar amounts.