WASHINGTON -- Among healthy people over the age of 75 who have the genotype associated with higher risk for Alzheimer's, low levels of vitamin B12 are associated with significantly worse performance on memory tests. This finding is published in the April issue of Neuropsychology, which is published by the American Psychological Association (APA). David Bunce, PhD, a psychologist at Goldsmith's College, University of London, Miia Kivipelto, PhD, MD, of the Aging Research Center at the Karolinska Institute in Stockholm and the Stockholm Gerontology Research Center, and Åke Wahlin, PhD, a psychologist at the University of Stockholm, conducted the study as part of a long-term multidisciplinary project that follows older people living in Stockholm's Kungsholmen parish.
Low Vitamin B12 Is Associated With Poorer Memory In Older People With High Risk For Alzheimer's
Scientists already knew of a genetic predisposition for Alzheimer's disease, and that low levels of two B vitamins-- B12 and folate--were also linked to problems. However, few had examined nutrition and genotype together relative to cognition, to reflect what real people carry into old age – a mix of inborn traits and environmental factors such as nutrition, including undiagnosed vitamin B deficiencies.
The apolipoprotein E gene, which moves cholesterol in the body, has a version called the є4 allele. Carried by perhaps 15 percent of the population, it is a risk factor for dementia. Current data collected over a six-year period suggests that nearly one out of four carriers with one copy of this allele and nearly half carrying two copies will develop Alzheimer's disease. Non-carriers also can get Alzheimer's.
Carriers of the є4 allele have smaller hippocampi, brain areas associated with memory, so the researchers wanted to measure how an additional physiological shortfall such as low Vitamin B, affected this particular group -- given that reduced B12 and folate have been linked generally with diminished memory and increased risk for Alzheimer's. Perhaps 10 percent of adults aged 75 years and older have low B12 or folate.
Bunce, Kivipelto and Wahlin studied 167 healthy older people, averaging nearly 83 years old. First, they checked blood samples for vitamin levels and genotype. Some 82 participants had low B12 (28 with the є4 allele; 54 without). The researchers then tested episodic memory, varying the test conditions to make them as sensitive as possible to underlying disorder.
Among carriers of the є4 ApoE allele, people with normal B12 levels recalled a greater number of words. More time to encode (five as opposed to two seconds) also was associated with greater recall. More than doubling encoding time strengthened memory more for the є4-low vitamin group than it did for other participants.
A significant difference showed up in the experiment's most demanding condition, when participants had just two seconds to encode words. In that situation, the high-risk genotype plus low B12 levels was significantly associated with poorer memory.
The findings endorse a complex model of vulnerability in which genetic and non-genetic factors interact. According to the authors, "є4 ApoE carriers may derive relatively greater cognitive benefits from B12 and folate supplements. Supplement treatment is relatively inexpensive and may be required as part of preventive health regimes for older persons."
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