Many older people have low vitamin D levels. A new study has found a link between vitamin D deficiency and an accelerated decline in loss of memory and cognitive ability.
Researchers at the University of California at Davis's Alzheimer's Disease Center looked at the association between blood levels of vitamin D and changes in memory and thinking ability in 382 adults over an average of just under 5 years. The participants averaged 76 years old in age, and the group included 158 whites, 113 African Americans and 96 Hispanics. A little less than 18% had dementia, 33% had mild cognitive impairment, and 50% were normal.
The researchers looked at blood levels of 25-hydroxyvitamin D (25-OHD), which is the form into which the body converts the vitamin D made by skin when exposed to sunlight and the form consumed in foods like eggs, oily fish, and dairy foods. Current recommendations are that 25-OHD levels in the blood should be between 20 and 50 nanograms per milliliter (ng/mL). Low levels are 12 to 20 ng/mL, and levels below 12 ng/mL are considered deficient.
More than 60% of the participants had low vitamin D levels. More than a quarter had a 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.
The study found that participants with dementia had lower vitamin D levels than those with mild cognitive impairment or whose memory was normal. Over the course of the study individuals with low vitamin D levels had a more rapid decline in cognitive function and in the ability to recall past personal experiences.
When the researchers controlled for other factors that affect memory and thinking, such as vascular disease, obesity, and a gene variant linked with Alzheimer's disease, the link between low vitamin D and cognitive impairment remained.
Half of Americans over age 65 have insufficient or deficient levels of vitamin D; Non-whites are more likely to have levels that are too low, the study noted. Previous research has linked low vitamin D levels to a higher risk of dementia and significant problems in memory and managing overall thinking processes.
The study was published in JAMA Neurology.