Do You Need More Vitamin D? – WebMD (blog)

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By Matt McMillen
WebMD Health News

We’ve heard that vitamin D is important, but just how important is it, and how much do we really need? Although study after study has linked a variety of ailments to vitamin D deficiency, others have warned against taking too much and questioned its health benefits.

The latest study, published in the journal Neurology, calls attention to the vitamin’s importance and its potential role in brain function.

To better understand its role in our health, we turned to vitamin D expert Clifford Rosen, MD, director of clinical and translational research and a senior scientist at Maine Medical Center’s Research Institute in Scarborough, Maine.

WebMD: Why do we need vitamin D? What does the latest research tell us about its importance?

Rosen: We need vitamin D because it promotes healthy absorption in the gut. Without it, you would need to take much more calcium into your system to maintain bone strength. Vitamin D quadruples your ability to take calcium into your intestines. It would be very difficult to maintain the level of calcium your bones need without vitamin D. There’s also some evidence that suggests it helps regulate immune cells and immune function, so it may have a role in immunity as well. In the study just published, the researchers measured the participants’ vitamin D and then followed them and looked for evidence of cognitive dysfunction. The problem with the paper is that it’s an association. It does not show cause and effect.

WebMD: Are we getting enough vitamin D? What happens if we don’t get enough?

Rosen: I think so. The vast majority of people, except for the elderly, do. The average level in the United States is about 25 nanograms per milliliter, which is considered sufficient. There’s probably a relatively small percentage that don’t, but most people can get it from sunlight and skin conversion of vitamin D and some from their diet.

If you don’t get enough, you could have bone loss, you could have fractures, and in older people you could have reduced muscle strength as well.

WebMD: Do our vitamin D needs change as we age?

Rosen: Probably not. It is just that we are not getting the types of things that we need as we age to maintain adequate vitamin D levels. Going outside and exercising, running for example, for just 10 minutes a day, you get plenty of vitamin D, but most people who are elderly are not out there exercising, they’re not getting sunlight, or they are protecting themselves from sunlight exposure. It’s the same thing with nutrition. If you decrease your intake of food, you are more than likely going to have a lower level of vitamin D, and as you age you have less appetite. It’s all about the function of aging that results in your vitamin D levels going down rather than aging per se.

If you measure vitamin D in older people, you’ll find that those with lower levels are sicker in general, but it’s not clear that the lower level of vitamin D is causing that. It may be that sickness is contributing to that lower level.

WebMD: Who should be taking vitamin D supplements? What determines that?

Rosen: The Institute of Medicine generally recommends 600 to 800 units per day. Older people, people in nursing homes or rehabilitation units, should get 800 units per day. For people who are young and healthy, there’s really no need for vitamin D supplements. They get enough from sunlight and diet. Normally, you can get about 300 units from diet, if, for example, you’re drinking some milk, which is fortified with vitamin D, and the rest from sunlight. There are some people with intestinal disorders, liver disease, or kidney disease for whom vitamin D supplementation is essential. But in the general population, it’s probably not that important.

WebMD: What are the most pressing questions that vitamin D researchers hope to answer?

Rosen: I think the biggest question is: Does it reduce falls in older people? That’s a really important question because falls lead to fractures and falls lead to serious secondary illnesses. So does vitamin D help prevent falls? Also, does vitamin D reduce the risk of cancer? Does vitamin D reduce the risk of heart disease? Those need to be addressed by large studies, which are ongoing right now, but we don’t have the answers yet. We have associations, but we don’t have cause and effect.

WebMD: Some recent studies, including one on bone health, failed to show that vitamin D supplements provide a benefit. Can you comment?

Rosen: If I were to summarize, the best evidence to date regarding vitamin D supplementation is with fractures in elderly people, but that effect is really small, and supplementation is really not doing anything in healthy individuals. Our sense is that there’s going to be variability in the outcomes of these studies, because of their small size. We really won’t know until we learn the results of the VITAL trial [a large vitamin D and omega-3 study, with more than 25,000 adults] in the next year to year and a half. That’s why the NIH funded the VITAL trial – to be a bit more conclusive about the effects. What we see now is that the effect is small, and it could be non-existent once we test it in a larger population.

WebMD: Can you get too much vitamin D? What are the risks?

Rosen: You can have high blood calcium from taking too much vitamin D, but that’s very unusual. Generally, we don’t recommend over 10,000 units of vitamin D per day because of that risk. In general, though, we think it’s pretty safe in the range of 1,000, 2,000, 3,000 units per day, but as it goes higher, so does the risk of kidney stones and high blood calcium.

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