原文报道
Vitamins D & E show brain benefits
By Stephen Daniells, 15-Jul-2010
Related topics: Research, Antioxidants, carotenoids, Vitamins & premixes, Cognitive and mental function
Eating food rich in vitamin E may reduce the risk of developing dementia, while insufficient levels of vitamin D may increase the risk of cognitive decline, say two new studies.
People who consumed the highest average intakes of vitamin E from the diet were 25 percent less likely to develop dementia than people with the lowest average intakes, according to new data published in the Archives of Neurology.
The benefits are reportedly related to the antioxidant activity of vitamin E, postulate scientists from the Erasmus Medical Center in Rotterdam, the Netherland, which counters the oxidative stress induced by a build up of beta-amyloid protein.
The build-up of plaque from beta-amyloid deposits is associated with an increase in brain cell damage and death from oxidative stress. This is related to a loss of cognitive function and an increased risk of Alzheimer's, the most common form of dementia and currently affects over 13 million people worldwide.
The direct and indirect cost of Alzheimer care is over $100 bn ( 81 bn) in the US, while direct costs in the UK are estimated at ?15 bn ( 22 bn).
The study follows hot on the heels of findings from a Swedish study, published in the Journal of Alzheimer's Disease, which found that a combination of different vitamin E forms could help prevent cognitive deterioration in advanced age.
There are eight forms of vitamin E: Four tocopherols (alpha, beta, gamma, delta) and four tocotrienols (alpha, beta, gamma, delta). Alpha-tocopherol (alpha-Toc) is the main source found in supplements and in the European diet, while gamma-tocopherol (gamma-Toc) is the most common form in the American diet.
Tocotrienols are only minor components in plants, although several sources with relatively high levels include palm oil, cereal grains and rice bran.
Study details
For the new study, the Rotterdam-based scientists analysed data on the intakes of antioxidants C vitamins C and E, beta-carotene and flavonoids C in 5,395 people aged 55 and older. Questionnaires and meal-based checklists were used to establish intakes of these micronutrients.
The participants were followed for about 10 years, during which 465 people developed dementia, of which 365 cases were for Alzheimer's disease.
After crunching the numbers, the researchers calculated that people with an average intake of 18.5 milligrams of vitamin E per day were 25 percent less likely to develop dementia than the people with an average of 9 milligrams per day. On the other hand, no associations were observed for dietary intake levels of vitamin C, beta-carotene and flavonoids.
"The brain is a site of high metabolic activity, which makes it vulnerable to oxidative damage, and slow accumulation of such damage over a lifetime may contribute to the development of dementia," wrote the authors.
"In particular, when beta-amyloid (a hallmark of pathologic Alzheimer's disease) accumulates in the brain, an inflammatory response is likely evoked that produces nitric oxide radicals and downstream neurodegenerative effects. Vitamin E is a powerful fat-soluble antioxidant that may help to inhibit the pathogenesis of dementia."
D and cognitive decline
The current issue of the Archives of Internal Medicine also carries new data from British researchers, who report that seniors with low levels of vitamin D may be at an increased risk of cognitive decline.
Our cognitive performance declines naturally as we age, but new data from David Llewellyn and his colleagues at the University of Exeter in England indicated that insufficient levels of vitamin D may accelerate this decline.
The Exeter-based scientists analysed vitamin D levels from blood samples of 858 adults aged 65 or older. Cognitive tests were undertaken at the start of the study, and again after three and six years.
The data showed that severe vitamin D deficiency, defined as blood levels of 25-hydroxyvitamin D (25(OH)D) of less than 25 nanomoles per liter - were associated with a 60 percent increase in the risk of substantial cognitive decline.
"If future prospective studies and randomized controlled trials confirm that vitamin D deficiency is causally related to cognitive decline, then this would open up important new possibilities for treatment and prevention," concluded Llewellyn and his co-workers.
In an accompanying editorial, Andrew Grey and Mark Bolland from the University of Auckland said it was now time to test the various hypotheses generated by observational studies of vitamin D in order to establish the potential public health benefit of raising vitamin D levels.
"Very importantly, such trials will also provide an opportunity to systematically assess potential harms of vitamin D supplementation, an issue that has been largely overlooked or dismissed. We should invest in trials that provide the best possible evidence on the benefits and risks of vitamin D before we invest in costly, difficult and potentially unrewarding interventional strategies, wrote Grey and Bolland.
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