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Too high vitamin D levels increase fatal cardiovascular disease rates

Vitamin D3
According to some vitamin experts, it's almost impossible to take so much vitamin D that you'll affect your health negatively. When it comes to vitamin D, the age-old adage is 'more is better'. Danish researchers have published the results of an epidemiological study which suggest otherwise, however, and which show that people with relatively high levels of vitamin D in their blood die more frequently from cardiovascular disease.

Vitamin D
If we are to believe some vitamin experts, vitamin D only becomes toxic at a concentration of 250 nanomoles per litre in the blood. Add to that the fact that the average Northerner has a vitamin D level of somewhere between 20 and 40 nanomoles per litre, then you'd probably tend to think that toxic levels are not so easily reached.

The same average Northerner would need to take 2000 IE or 50 micrograms of vitamin D3 daily to reach and maintain a level of 80 nanomoles per litre. In countries like the US and Canada, doctors advise people not to take more than 50 micrograms vitamin D3 per day.

Some vitamin experts have expressed their indignation at the 'outdated' European and American recommendations. We should all have a vitamin D level of somewhere between 100 and 200 nanomoles per litre, they say; then we'd be more healthy. So we should be taking even more supplements.

The Danes, working at the University of Copenhagen, have published an analysis in the Journal of Clinical Endocrinology and Metabolism of data gathered during the Copenhagen Vitamin D Study in the period 2004-2010. The researchers used data on 243,672 participants.

During the study 16,645 participants died. The most important causes of death were cardiovascular diseases, which caused 5,474 of the fatalities.

The Danes discovered that both low and high concentrations of vitamin D raised the risk of mortality from cardiovascular diseases. The first figure below refers to all participants in the study; the second shows the data split for men and women.

In both cases a vitamin D level of 70-80 nanomoles per litre is optimal, and the risk of a fatal heart attack or stroke rises the further the vitamin D level deviates from the optimal level.

Too high vitamin D levels increase fatal cardiovascular disease rates

The researchers suspect that when the vitamin D level is too high, cells in the blood vessel walls start to accumulate calcium, which leads to narrowing and calcification of the arteries.

To make it clear: the Danish study doesn't mean that vitamin D supplementation is therefore unhealthy. The group of people with a too high vitamin D status is small compared to the group with too little vitamin D in their blood, and the negative effect of a serious vitamin D deficiency is much bigger than the negative effect of an excess of vitamin D. But the Danish study does lead to the suspicion that long term high doses of vitamin D supplements without medical supervision are not a good idea.

Watch this space.

J Clin Endocrinol Metab. 2015 Jun;100(6):2339-46.

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