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Putting the ‘D’ in Diabetes

Low levels of vitamin D have long been known to predispose to osteoporosis and rickets in children. It’s for this reason that mothers used to spoon feed cod liver oil, a rich source of vitamin D, to their unwilling children. Nowadays we supplement milk products with extra vitamin D, sparing legions of kids from the horrors of cod liver oil, which tastes about as bad as it sounds. Now, evidence is emerging that vitamin D may help prevent the onset of type 1 diabetes as well.

This finding has actually been anticipated for some time. Giving mice a drug called streptozotocin can cause type 1 diabetes, but pretreatment with vitamin D can forestall the appearance of the disease. A few small studies have also shown that kids who took extra vitamin D or who ate cod liver oil had lower rates of type 1 diabetes. A recent issue of The Lancet reports a large study performed in Finland that confirms these results. Researchers asked women who had children in the 1960’s whether they gave their kids extra vitamin D or not. Then they looked at whether these kids developed type 1 diabetes over the next twenty years or so. The results showed that kids who got extra vitamin D were about five times less likely to develop diabetes, while kids with very low levels of vitamin D (as seen by the fact that they actually developed rickets, a bone disorder that occurs when vitamin D levels are too low) got diabetes at three times the normal rate.

Now, a few caveats are in order. First of all, this was a retrospective analysis that required women to remember whether they gave vitamins to their kids twenty years earlier. Also, the study took place in Finland, where there are only two hours of daylight in the winter months. Low levels of sunlight are associated with low levels of vitamin D. Therefore, it’s very unclear whether these results will apply to folks who live in sunnier climates. Finally, this was not a treatment-based study. What we really need is for someone to take a couple of thousand babies, give half of them extra vitamin D, and show that they get less type 1 diabetes. It’s unclear if such an experiment will ever be done, but even if it were started yesterday, it would still take about 20 years to get the answer.

So what do we do in the meantime? Should we be giving kids extra vitamin D? Well first of all let’s make it clear that there aren’t clear Recommended Daily Allowances for vitamin D in kids or adults, at least in this country. In other countries (such as Finland), the RDA for vitamin D in kids used to be about 4,000 IU (International Units). Over the years it dropped to 2,000 IU (which is what it was in the 1960’s, when it would matter for the study we talked about above), then 1,000 IU, then down to 400 IU. In fact 400 IU is still the standard in most places, and is the amount of vitamin D found in one adult multivitamin tablet. Clearly, everyone should get at least that amount, and probably more if they get less sunlight than usual, either because they’re elderly, or they live in northern latitudes, or because they like to watch cartoons instead of playing outside.

Don’t overdo the vitamin D, though, as too much can cause problems ranging from confusion to constipation, vomiting, and weakness.Stick to one or two multivitamins worth, and you (and your kids) will be fine.

The final question concerns the way vitamin D might have an effect on diabetes. At this point, we really don’t know how this works. Vitamin D raises calcium levels in the body, but researchers have found that this has nothing to do with the effect on diabetes. Interestingly, we know that type 1 diabetes occurs when the immune system attacks the insulin-producing beta cells of the pancreas, and vitamin D has been shown to tamp down the immune response in several important ways. Given that most of the other immunomodulatory drugs under investigation can be quite toxic, vitamin D looks like a very attractive treatment if it turns out to work.

References:

1. Hypponen E, Laara E, Reunanen A, Jarvelin MR, Virtanen SM. Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study. Lancet. 2001; 358: 1500-3.

2. Riachy R, Vandewalle B, Belaich S, Kerr-Conte J, Gmyr V, Zerimech F, d’Herbomez M, Lefebvre J, Pattou F. Beneficial effect of 1,25 dihydroxyvitamin D3 on cytokine-treated human pancreatic islets. Journal of Endocrinology. 2001 169: 161-8.

3. Stene LC, Ulriksen J, Magnus P, Joner G. Use of cod liver oil during pregnancy associated with lower risk of Type I diabetes in the offspring. Diabetologia. 2000; 43: 1093-8.