Sunshine is a natural source of vitamin D – and the question is whether it can really kill. The jury is still out on that one. A Danish scientist says it’s too early to say which form of vitamin D is associated with increased mortality rates. (Photo: Colourbox)

Too much vitamin D can kill you

In recent years vitamin D has become known as a super vitamin. But now a study of a quarter million Danes reveals a link between too much vitamin D and excess mortality.

There have been plenty of success stories about vitamin D in the media in the past few years. Not only does it guide calcium to our bones, it’s also good for fighting off cardiovascular diseases, depression and even cancer.

However, a brand new study now also shows a correlation between vitamin D intake and excess mortality.

The startling new findings, just published in the Journal of Clinical Endocrinology and Metabolism, comes from Darshana Durup, a PhD fellow at the Faculty of Health Sciences at the University of Copenhagen.

Low and high vitamin D levels are harmful

”We found that there is an increased mortality in people with low levels of vitamin D – but surprisingly enough this is also true for people with high vitamin D levels,” says Durup.

We found that there is an increased mortality in people with low levels of vitamin D – but surprisingly enough this is also true for people with high vitamin D levels.

Darshana Durup

“We can draw a curve, suggesting that perhaps too little and too much are both harmful.”

Her research shows that a high concentration of 140 nanomoles of vitamin D per litre of blood (see Factbox) increases the mortality by a factor of 1.42.

A low concentration of 10 nanomoles per litre of blood increases the mortality rate by a factor of 2.31.

The optimal amount of vitamin D per litre of blood appears to be 50 nanomoles: at this level, the study found the lowest mortality rates.

Solid research

The concentration of vitamin D is measured in nanomoles.

It is normally assumed that vitamin D concentration increases by around 3 nanomoles per litre of blood for every 2.5 micrograms of vitamin D intake.

The Danish Health and Medicines Authority recommends at least 7.5 micrograms of vitamin D per day. For instance, 100 grams of smoked herring contains 8 micrograms of vitamin D.

Click here for a list of vitamin D content in other types of food.

This is a comprehensive study, based on blood samples from more than a quarter of a million Copenhageners, who have visited a doctor for general health reasons, and who at the same time had their vitamin D levels checked.

According to Durup, the findings fuel an important argument against those who believe that we cannot get too much vitamin D.

“There is no scientific support for the ‘the more, the better’ argument when it comes to vitamin D, and our study doesn’t support that argument either,” she says.

“There has been a lot of research into the effects of low vitamin D levels. But with this study, we hope to inspire further research into the cause of increased mortality with high levels of vitamin D.”

Heated Vitamin D debate

This study is part of the so-called CopD project – an acronym for the Copenhagen Vitamin D Study.

The study is based on 247,574 Copenhageners as test subjects.

Here she is treading in a minefield: as the popularity of vitamin D has exploded in recent years, the medical debate has become overheated.

Health authorities in both the US and in Denmark are under great pressure from vitamin D proponents among physicians and the pharmaceutical industry to increase the recommended doses of the vitamin.

A leading American figure in the vitamin D debate, Dr Clifford Rosen, recently armed himself with the existing research and advised the US Food and Drug Administration to be critical of the vitamin.

This led to an onslaught of hate mail from disagreeing colleagues – mails of a professional as wells as a highly personal nature.

Vitamin studies require humility

Darshana Durup’s experiences with the Danish debate are somewhat less harsh, but since this is a sensitive issue, she speaks with caution:

“We have moved into a controversial area. This is because the climate debate and research in nutrition arouses many emotions,” she says.

“That’s why it’s really important for me to stress that even though our research suggests a link between too much vitamin D and high mortality rates, there is still no explanation of why this is so.”

She is also keen to point out that there’s still a higher mortality associated with too little vitamin D than with too much. And out of the quarter million people that she’s helped examine, there were more who lack vitamin D than there were of those who have too much of it.

Some 2,500 of the test subjects had too much vitamin D, whereas more than 20,000 had too little.

Excessive levels could have a variety of causes

Another reason why Durup is being cautious is that we get vitamin D from food, sunshine as well as from vitamin supplements. But the only thing her research shows is that the 2,500 people had too much of vitamin D – not why they had too much of it.

Her scientific ambition is therefore to learn more about why there is this link between excessive vitamin D levels and increased mortality rates.

“Now we need to start looking at whether we can correlate all these blood samples with various disease registries – including cancer registries. We are already working with the Danish Cancer Society,” says Durup.

“In that way we can compare the prevalence of vitamin D in people with different diseases and different causes of death and thus gain a more detailed insight into how the vitamin is linked to illness and mortality," says Durup.


Read this article in Danish at

Translated by: Dann Vinther

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