B12 supplements needed in those at high risk for Alzheimer's
older people with high risk for Alzheimer's, according to a large
Swedish study, thought to be one of the first to examine how the
relationship between diet and genes can affect cognition in old
age.
The researchers found that in healthy people over the age of 75 who have the genotype associated with higher risk for Alzheimer's, low levels of vitamin B12 were associated with significantly worse performance on memory tests.
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.
Scientists are increasingly looking to genetics, or 'nutrigenomics', as a way of looking more closely at individual nutritional needs. A recently presented study suggested that fruit and vegetables could offer higher protection against breast cancer in people with a particular genetic make-up.
The new research, by David Bunce from Goldsmith's College, University of London, Miia Kivipelto, of the Aging Research Center at the Karolinska Institute in Stockholm and the Stockholm Gerontology Research Center, and åke Wahlin, a psychologist at the University of Stockholm, was part of a long-term multidisciplinary project that follows older people living in Stockholm's Kungsholmen parish.
The team notes in the April issue of Neuropsychology(vol 18, no 2) that the apolipoprotein E gene, which moves cholesterol in the body, has a version called the ?4 allele. Carried by perhaps 15 per cent 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 ?4 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 per cent of adults aged 75 years and older have low B12 or folate, they suggest.
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 ?4 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 ?4 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 ?4-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, "?4 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".
