Study Links Low Vitamin D, Dementia Risk

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Harvard Medical School
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Study Links Low Vitamin D, Dementia Risk

News Review from Harvard Medical School

August 7, 2014

News Review From Harvard Medical School -- Study Links Low Vitamin D, Dementia Risk

Older adults who have low blood levels of vitamin D may be more likely to develop dementia, a study suggests. The analysis is based on data from a study of heart health. Researchers gave tests of mental function to more than 1,600 adults age 65 or older. They also measured vitamin D levels in the blood. They repeated the tests of mental function 6 years later. The new study analyzed the links between vitamin D levels and dementia risk in this group. People with low levels of vitamin D were 70% more likely to develop Alzheimer's disease as those with normal levels. Those with very low vitamin D levels were more than twice as likely to develop Alzheimer's. Results were similar for the risk of dementia from all causes. People with low levels of vitamin D had a 53% higher risk of dementia. Those with very low levels had more than twice the risk. The journal Neurology published the study. HealthDay News wrote about it August 6.


By Robert H. Shmerling, M.D.
Harvard Medical School


What Is the Doctor's Reaction?

Not long ago, vitamin D was thought to be good for your bones -- and little else.

That's changed. Now you can find claims that vitamin D is good for just about everything. Most remain unproven. Deficiency of vitamin D has been linked to:

  • Cancer
  • Poor immune function
  • Dementia
  • Arthritis

Past studies have linked lower intake or lower blood levels of vitamin D with dementia. But the lower vitamin D levels in people with brain disease could be the result of the disease rather than a cause of it.

We need studies that examine people with normal brain function who develop dementia over time. Prior studies have not reached clear conclusions.   

That's where a new study comes in. It included more than 1,600 elderly men and women (average age: 74) with normal brain function. They were assessed for dementia over time and had tests of their blood vitamin D levels. Over 6 years:

  • Those with a low vitamin D level had a 53% higher risk of developing dementia than those with normal levels.
  • Among those with the lowest vitamin D levels, the risk of developing dementia was 125% higher than for those with normal levels.
  • The results were similar for Alzheimer's disease: a 70% higher risk with low vitamin D and 120% higher risk with very low levels.

These findings held up even after accounting for other factors that might contribute to dementia risk, such as smoking or drinking a lot of alcohol.

But this type of study cannot determine whether the low vitamin D levels actually caused dementia. We also don't know from this study whether increasing vitamin D levels (through diet or supplements) might have prevented dementia.

Still, the findings would fit with the idea that vitamin D may help the brain to function normally and that getting enough vitamin D is one way to reduce the risk of dementia.

Why should vitamin D affect brain function? The answer isn't clear. But here are some findings of related research:

  • A protein that grabs onto vitamin D (called a receptor) and an enzyme that creates the active form of the vitamin are found in the brain.
  • Stroke seems to be more likely among those who are deficient in vitamin D.
  • In the lab, vitamin D encourages white blood cells to remove a protein (called amyloid) considered important in the development of Alzheimer's disease. The vitamin also protects brain cells from amyloid-related damage.
  • In rats, vitamin D can slow age-related declines in learning and memory.

Taken together, this research suggests that vitamin D is doing something vital in the brain. That makes this new study's findings even more intriguing.


What Changes Can I Make Now?

The role of vitamin D in conditions other than bone health remains a matter of some debate. Still, there seems to be little harm linked with keeping your vitamin D in the normal range.

You may be at particular risk of vitamin D deficiency if you:

  • Are elderly
  • Are obese
  • Have chronic (long-term) disease of the digestive system (such as Crohn's disease or celiac disease) or kidneys
  • Have low vitamin D in your diet
  • Have dark skin
  • Don't get much sun exposure

You can take steps to avoid vitamin D deficiency:

    • Check food labels and choose foods that are high in vitamin D. These include:
      • Fish (especially fatty fish, such as tuna, salmon and mackerel)
      • Eggs
      • Milk, cheese and other dairy products
      • Fortified cereals
    • Consider taking a supplement. A common amount recommended for adults is 1,000 International Units (IU) per day. But guidelines vary depending on age, diet, medicines taken and other health problems. Check with your doctor first. 
    • Get some sun. The UV rays of the sun convert an inactive form of vitamin D in the skin to an active form. This means that sun exposure can help maintain vitamin D levels. About 10 to 15 minutes a day may be enough. Be careful, though. Too much sun can damage skin and increase the risk of skin cancer.
    • Have your blood tested. Doctors do not routinely check vitamin D levels. However, it's important to do so if a person has osteoporosis, unexplained bone fractures or symptoms (such as bone pain) that might be related to low levels of vitamin D.

It is unusual to get too much vitamin D from the sun or from dietary sources. However, it can happen if you get too much in supplements. Avoid a dose higher than 4,000 units per day. That's the "tolerable upper intake level," according to the Institute of Medicine.


What Can I Expect Looking to the Future?

We need more research that compares large groups of people at risk for dementia who do or don't take vitamin D pills. Such research would need to include blood vitamin D levels before and after the study. If vitamin D treatment and avoiding vitamin D deficiency are linked to lower rates of dementia, we would have further evidence that low vitamin D might actually cause dementia and that increasing blood levels may be protective.

There is currently no known cause for most cases of dementia and no highly effective treatment. So the impact of such research findings could be enormous.

Last updated August 07, 2014

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