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Vitamin D and the link with longevity

BMJ Group News

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Researchers have found a link between a person’s vitamin D levels and how likely they are to die early. But we don’t know if having low vitamin D actually plays a role in people dying early, or if taking vitamin D supplements would help.

What do we know already?

Our bodies need a certain amount of vitamin D to stay healthy. We can get vitamin D from some foods, or from taking supplements. However, most of the vitamin D we need can be made from sunlight, which the cells in the skin can use to make vitamin D.

People who don’t get that much exposure to sunlight - such as people who don’t spend much time outdoors, people who live in parts of the world without much sunshine, or who cover their skin for cultural reasons - often have lower amounts of vitamin D than others. Previous studies have suggested that having a low amount of vitamin D in the blood is linked with heart disease, cancer, and dying early. But the results of previous studies have been mixed.

How was the new study done?

This new study pooled the results of seven studies of 26,000 older adults. In each of the studies, researchers measured how much vitamin D people had at the start of the study and then recorded how many people died during the studies. The researchers then looked for a link between vitamin D levels and the chances that people died early.

What does the new study say?

During the studies, the longest of which lasted about 16 years, around 7,000 people died. The researchers adjusted the figures to allow for the differences in vitamin D according to people’s age, sex, and the time of year they had their vitamin D levels measured. After this adjustment, the results showed that people who had the lowest amount of vitamin D in their blood were more likely to die early than people who had the most vitamin D.

How reliable is the research?

Pooling different studies can be a reliable way of looking at results. But this is only reliable when all the studies are done in more or less the same way and are designed to look at the same things. This has been a big problem with earlier studies of vitamin D and health. In this case the eight studies were broadly similar, so this is an improvement on previous studies.

There are other things that could have affected the results. The researchers did account for the effect of people living in different countries but not different regions. Being in a more northerly region of the same country, for example, might mean you get less sunlight and this can affect vitamin D levels.

There is a limit to how much we can draw from these results. This type of study does not show that having low vitamin D levels causes people to die early. And even if we knew for certain there was a link between vitamin D and dying early, we don’t know whether taking vitamin D supplements would help people to live longer.

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