A strong link in the diet-memory connection seems to be with the B vitamins: folic acid and vitamins B6 and B12. These vitamins are not naturally produced within the body and must be obtained from food or supplements. B-complex vitamins are found in brewer's yeast, liver, whole-grain cereals, rice, nuts, milk, eggs, meats, fish, fruits, leafy green vegetables, and other foods. People with deficiencies in some or all of these vitamins are at greater risk of age-related memory impairment as well as dementia. Your daily intake of these nutrients should be 400 micrograms of folic acid, 1.3 to 1.7 milligrams of vitamin B6, and 6 micrograms of vitamin B12. But be careful with B6 supplementation because excessive amounts can cause a peripheral neuropathy (numbness and tingling in the fingers and toes).
Vitamin B12 keeps neurons healthy by helping to make and preserve myelin, the fatty sheath that surrounds and protects axons. A deficiency of vitamin B12 can cause permanent damage to neurons, leading to memory loss, as well as slowing down your thinking and making you feel fatigued. Vitamin B12 deficiency becomes more common with age. Smoking and drinking also increase the risk of this vitamin deficiency.
Fortunately, vitamin B12 deficiency is easy to detect with a blood test and easy to correct with monthly injections of the vitamin. The injections can help prevent further memory impairment, but they often won't restore what's been lost. In most cases, it doesn't help to take vitamin B12 supplements orally if you have a deficiency because the most common cause is malabsorption, an inability to absorb the vitamin via the digestive process.
The Homocysteine Link. Another, more complex link in the connection between the B vitamins and memory loss has to do with homocysteine, an amino acid in the blood that's been getting a lot of attention lately.
Several years ago, evidence began mounting that a high level of homocysteine was a major risk factor for heart disease, stroke, and peripheral vascular disease. Then came evidence that a high homocysteine level was toxic to neurons and a strong risk factor for Alzheimer's disease and other forms of dementia. One cause of elevated homocysteine is a deficiency in folic acid and vitamins Bfi and B 12, which normally assist in the breakdown of homocys-teine in the blood.
Your doctor can measure your homocysteine level with a blood test. Testing is particularly indicated for people at risk for stroke or heart attack, such as those with a personal or familial history of cardiovascular disease. Though there is no official cutoff level, research suggests that readings below 12 micromoles per liter are desirable. In a study in the Annals of Neurology in 2003, the risk of cognitive decline over the course of three years was nearly threefold among adults with homocysteine levels above 15 compared with people with lower levels.
We know that getting the recommended amounts of B vitamins, either through a healthy diet or supplements, can lower homocysteine levels. Keeping homocysteine low can probably help protect you against cognitive decline. What remains to be seen is whether increasing your intake of B vitamins can stabilize or reverse cognitive decline.
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