Vitamin D and Alzheimer's Disease: What's the Connection?
Could getting enough vitamin D help prevent Alzheimer's disease and other forms of dementia? Years of research, including a recent large study, have uncovered an association between low vitamin D levels in adults and higher rates of numerous medical problems, including Alzheimer's disease.
Vitamin D in the Blood
The 2014 study in Neurolog, which followed more than 1,600 men and women for five years, found that participants whose levels of vitamin D were less than 50nm (nanomoles) per milliliter of blood were twice as likely to develop dementia and Alzheimer's disease. The lower the vitamin D levels, the higher the risk. The range of vitamin D considered normal is 74 to 184 nanomoles (which is the equivalent of 30 to 74 nongrams, the unit used by the National Institutes of Health).
Vitamin D in the Body and Brain
The presence in the brain of a protein known as beta-amyloid can lead to the plaque formation (the buildup of beta-amyloid and other substances) that is characteristic of Alzheimer's and differentiates the disease from other types of dementia, the deterioration of intellectual functioning most commonly seen among the elderly. According to Oleg Tcheremissine, MD, Research Director in the Department of Psychiatry and Behavioral Sciences at Carolinas Medical Center in Charlotte, NC, vitamin D helps regulate various protective mechanisms in the brain, including the process by which certain protective cells clear beta-amyloid from the brain.
"Vitamin D plays a pivotal role in areas of the brain associated with memory and other cognitive skills," Tcheremissine points out. "But it also plays a critical role in cardiovascular [heart and blood vessel] health, which has also been shown to affect cognitive abilities."
Vitamin D Recommendations
Vitamin D is essential for strong bones and a healthy immune system. The Institute of Medicine (IOM) recommends a daily intake of 600mg vitamin D for children and adults up to age 70, and 800mg for those 70 and above. The IOM also recognizes a safe daily upper limit of 2,000 to 4,000mg. How much vitamin D is actually beneficial, and how much should come from supplements, however, are ongoing matters of debate.
Sources of Vitamin D
Vitamin D is a hormone produced by your body when ultraviolet rays from the sun penetrate your skin. In many people, however, this process is limited by factors such as darker skin pigmentation, the use of sunscreens, living at higher altitudes where exposure to daylight is insufficient, and the physical changes in skin and other organs that occur with aging. And ultraviolet radiation from the sun is a major cause of skin cancer, including potentially deadly melanomas.
Limited amounts of vitamin D are also supplied by foods such as salmon, herring, mackerel, and other fatty fish, and vitamin-fortified dairy and cereal products. With commercially fortified products, you can calculate the amount of vitamin D you're getting simply by looking at the product label.
Should You Take Supplements?
Unless you have severe liver, kidney, or gastrointestinal disease, you can probably take vitamin D supplements without any problems. Dosage is important for everyone, because vitamin D is a fat-soluble vitamin, which means that excess is stored in your body and can ultimately have toxic side effects. One such side effect is increased absorption of calcium, which can be beneficial in some circumstances but dangerous in others. Too much calcium can result in hypercalcemia, or too much calcium in the blood. This can cause kidney stones, weakened bones, and heart, muscle, and mental heath problems.
The real question is: Do you need vitamin D supplements and, if so, how much should you take? "A simple blood test can help determine if your blood levels of vitamin D are low," Tcheremissine points out. "If they are, you can discuss taking therapeutic doses of D3 [also known as cholecalciferol, and the form of vitamin D made by the body] supplements with your health care provider."
While study results have associated low blood levels of vitamin D with Alzheimer's disease, they do not yet confirm that low dietary intake of vitamin D actually leads to Alzheimer's disease, nor do they establish how much vitamin D from food or supplements might help prevent Alzheimer's disease or dementia. Tcheremissine acknowledges that much is still unknown. "In order to have any clinical benefit, future research must focus on early identification of those at risk and the most effective prevention strategies."