Low
vitamin D levels linked to faster memory loss in older adults Published
September 14, 2015.
Older
adults with low vitamin D levels - and that accounts for most of them - may
lose their memories and thinking abilities faster than those with normal
vitamin D levels, researchers say. "We were not particularly surprised by
our findings because there is a recent and growing literature on the
associations between vitamin D status and risk of Alzheimer's disease/dementia,
cognitive decline, and brain atrophy," Dr. Joshua W. Miller from Rutgers
University, New Brunswick, New Jersey said. Miller and a team at
University of California, Davis's Alzheimer's Disease Center looked at the
association between blood levels of vitamin D and changes in memory and
thinking ability in 318 adults over an average of five years. Participants were
an average of 76 years old, and included 158 whites, 113 African Americans and
96 Hispanics. Past research has shown that fully half of the U.S. population
over age 65 has insufficient or deficient levels of vitamin D, and that
non-whites are more likely to have levels that are too low, the authors point
out. Previous studies have also linked low vitamin D levels to higher risk of
dementia. Among people with cognitive impairment, an estimated 70 percent to 90
percent are insufficient in vitamin D. In the new study, the researchers
looked at blood levels of 25-hydroxyvitamin D (25-OHD), which is the form
generated when the body converts vitamin D made in the skin in response to
sunlight and consumed in foods like eggs, oily fish and milk. Circulating
25-OHD levels can only be measured by blood test, and current guidelines
consider adequate levels to be in the range of 20 nanograms per milliliter of
serum to 50 ng/mL. Insufficient is 12 to less than 20 ng/mL, and levels below
12 ng/mL are considered deficient. The study team found that more than 60
percent of the participants had low vitamin D levels, including more than a
quarter who had vitamin D deficiency. African Americans were more than three
times as likely and Hispanics were more than twice as likely as whites to have
low vitamin D levels. Individuals with dementia had lower vitamin D levels
(about 16.2 ng/mL) than those with mild cognitive impairment (average 20 ng/mL)
or whose memory was normal (19.7 ng/mL), according to the results. Low vitamin
D levels were also associated with significantly more difficulty with
remembering general information (semantic memory), seeing the relationship
between objects (visuospatial ability) and managing overall thinking processes
(executive function). Over a period of just under five years, individuals with
low vitamin D levels showed a more rapid decline in executive function and in
the ability to remember their own past personal experiences (episodic memory).
These rates of decline were similar for individuals who had normal brain
function at the beginning of the study and for those who already had dementia
or mild cognitive impairment. When the researchers adjusted for other cognitive
risk factors, such as vascular disease, obesity and the presence of a gene
variant associated with Alzheimer's disease risk, the link between low vitamin
D and cognitive impairment remained. "Low vitamin D status is very common
in older adults and is associated with accelerated rates of cognitive
decline," Miller said. So far, he added, there have been no careful
studies to determine whether taking vitamin D could slow or prevent memory
loss, but he suggested measuring your vitamin D level to see whether you need
more vitamin D. "There is a potential danger in consuming too much vitamin
D as a supplement," Miller cautioned. "The upper tolerable level of
daily intake (UL) for vitamin D established by the Institute for Medicine is
4000 IU/day for individuals age 9 years and older. Above this level, the risk
of adverse health effects increases, with very high doses (10,000 IU/day or
more) potentially causing damage to kidneys and other tissues. The recommended
dietary allowance (RDA) is 600 IU/day.
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