The researchers from Johns Hopkins Bloomberg School of Public Health and other institutions say such supplements may be an ideal prevention strategy for our aging population as they are relatively non-toxic and are thought to have wide-ranging health benefits.
There are nearly 18 million people with dementia in the world and the most common cause of this dementia is Alzheimer's disease. By 2025 this figure will rise to 34 million, with 71 per cent of these likely to live in developing countries.
Previous studies have shown that antioxidant vitamins may protect the brain against damage caused by free radicals and other reactive oxygen species - molecular byproducts of basic cellular metabolism. Neurons are especially sensitive to damage caused by free radicals, which is believed to be partially responsible for the development of Alzheimer's disease.
The researchers examined data from the Cache County Study, a large, population-based investigation of the prevalence and incidence of Alzheimer's disease and other dementias. Around 4,700 residents who were 65 or older were assessed from 1996-1997 and again from 1998-2000. Study participants were asked at their first contact about vitamin usage. The researchers then compared the subsequent risk of developing Alzheimer's disease over the study interval among supplement users versus nonusers.
Approximately 17 per cent of the study participants reported taking vitamin E or C supplements, write the researchers in this month's issue of the journal Archives of Neurology (2004;61:82-88) .These individuals were significantly more likely to be female, younger, better educated and reported better general health when compared to non-supplement users. In addition to those who took vitamin supplements, another 20 per cent of study participants used multivitamins, but without a high dosage of vitamin E or C.
The researchers reported a trend towards reduced Alzheimer's disease with a combination of vitamin E and C supplements, even after controlling for age, sex, education and general health.
"Use of vitamin E and C (ascorbic acid) supplements in combination reduced AD prevalence [by about 78 per cent] and incidence [by about 64 per cent]," the authors write.
However, there was no notable reduction in the risk of Alzheimer's disease with vitamin E or vitamin C alone or with multivitamins. Multivitamins typically contain the recommended daily allowance of vitamin E (22 IU or 15 mg) and vitamin C (75-90 mg), while individual supplements contain doses up to 1,000 IU of vitamin E and 500-1,000 mg or more of vitamin C.
The researchers explained that the use of vitamins E and C may offer protection against Alzheimer's disease when taken together in the higher doses available in individual supplements. In addition, there may be some protective effect with vitamin E when it is combined with the lower doses of vitamin C found in multivitamins.
"Further study with randomized prevention trials is needed before drawing firm conclusions about the protective effects of these antioxidants. Such trials should consider testing a regimen of vitamin E and C in combination. If effective, the use of these antioxidant vitamins may offer an attractive strategy for the prevention of Alzheimer's disease," writes lead author Dr Peter P. Zandi from Johns Hopkins Bloomberg School of Public Health.