A new study, published in The Journal of the American Medical Association this month, has found that high doses of three B vitamins: B6, B12, and folate, do not slow the progression of Alzheimer’s disease.
Researchers from the Department of Neurosciences at the University of California randomly assigned 340 participants suffering from mild Alzheimer’s disease into a high dose group and a control group. The high dose group received supplements containing 25 mg per day of vitamin B6, 5 mg per day of folate, and 1 mg per day of vitamin B12, around 20 times the recommended daily intake for these vitamins while the control group received identical placebos.
During the 18 month study period, the group who received the B-vitamin supplements showed similar cognitive decline as measured by the Alzheimer Disease Assessment Scale to those who received the placebo suggesting no benefit from the vitamin supplementation.
It had been theorized that an amino acid known as homocysteine may play a role in the progression of Alzheimer’s disease because higher than normal levels of homocysteine are found in the brains of Alzheimer’s disease sufferers. The B-vitamins play an important role in the metabolism of homocysteine and studies have found a directly correlation between a high intake of the B-vitamins and low levels of homocysteine in the blood. Studies have also found average levels of vitamin B12 to be much lower in Alzheimer’s disease sufferers compared to the general population.
The participants in the B-vitamin group did show a 31% reduction in homocysteine levels however this did not lead to a slower rate of cognitive decline in these patients.
Although B-vitamin supplementation did not slow the progression of Alzheimer’s disease, it is thought that maintaining low homocysteine levels throughout life may prevent Alzheimer’s disease from occurring in the first place. One study, published in the New England Journal of Medicine in 2002 found that individuals in the top 25% for plasma homocysteine levels were almost twice as likely to subsequently develop Alzheimer’s disease compared to the remainder of the population.
High homocysteine levels have been linked to an increased risk of atherosclerosis and cardiovascular disease. A history of cardiovascular disease is known to increase the likelihood of developing Alzheimer’s disease and vascular dementia later in life. High homocysteine levels may also increase the amount of oxidative damage and cell death occurring in the brain.
Rich sources of the B vitamins include potatoes, mushrooms, bananas, turkey, tuna, eggs, spinach, broccoli, asparagus, and yeast spreads such as marmite and vegemite.
Most people get a sufficient intake of the B vitamins through diet alone, however vitamin B6, B12, and folate are all well tolerated by the body at levels much higher that the RDA. The B vitamins are all water soluble so any excess amounts are excreted through urine.
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