Low levels of the sunshine vitamin were associated with a three times faster rate of cognitive decline than those with adequate vitamin D levels, according to findings published in JAMA Neurology.
The low vitamin D levels were associated with impaired performance, particularly in domains such as memory loss that are associated with Alzheimer’s disease and dementia, added the researchers.
“We expected to see declines in individuals with low vitamin D status,” said Charles DeCarli, director of the the UC Davis Alzheimer’s Disease Center. “What was unexpected was how profoundly and rapidly [low vitamin D] impacts cognition.”
The researchers said their findings amplify the importance of identifying vitamin D insufficiency among the elderly, particularly high-risk groups such as African-Americans and Hispanics, who are less able to absorb the nutrient from its most plentiful source: sunshine. Among those groups and other darker-skinned individuals, low vitamin D should be considered a risk factor for dementia, they added.
The sunshine vitamin
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
“This work, and that of others, suggests that there is enough evidence to recommend that people in their 60s and older discuss taking a daily vitamin D supplement with their physicians,” added Joshua Miller, professor in the UC Davis Department of Pathology and Laboratory Medicine at the time when the research was conducted and now professor and chair of the Department of Nutritional Sciences at Rutgers University..
“Even if doing so proves to not be effective, there’s still a very low health risk to doing it.”
Dr Miller and his co-workers analyzed data from 382 racially and ethnically diverse men and women (mean age of 76) in Northern California participating in longitudinal research at the Alzheimer’s Disease Center in Sacramento. Of the participants, 41% were white, 30% were African American, 25% were Hispanics, and 4% were from other racial/ethnic groups. The participants were either cognitively normal, or had mild cognitive impairment or dementia.
Baseline data showed that 26% of the participants were vitamin D deficient, while 35% were insufficient. Among Caucasians, 54% had low vitamin D, compared with 70% of African-Americans and Hispanics.
The rate of cognitive decline was found to be two-to-three times faster in the vitamin D deficient people over five years of study, compared to people with adequate serum vitamin D levels. In other words, it took only two years for the deficient individuals to decline as much as those with adequate vitamin D declined during the five-year follow-up period.
“Our data support the common occurrence of vitamin D insufficiency among older individuals,” wrote the authors in JAMA Neurology. “In addition, these data show that African American and Hispanic individuals are more likely to have vitamin D insufficiency or deficiency. Independent of race or ethnicity, baseline cognitive ability, and a host of other risk factors, vitamin D insufficiency was associated with significantly faster declines in both episodic memory and executive function performance, which may correspond to elevated risk for incident Alzheimer disease dementia.
“Given that vitamin D insufficiency is medically correctable, well-designed clinical trials that emphasize enrollment of individuals of nonwhite race/ethnicity with hypovitaminosis D could be useful for testing the effect of vitamin D replacement on dementia prevention.”
Dr DeCarli added: “This is a vitamin deficiency that could easily be treated and that has other health consequences. We need to start talking about it. And we need to start talking about it, particularly for people of color, for whom vitamin D deficiency appears to present an even greater risk.”
'Reflective of the diversity of the American population'
Commenting independently on the study's findings, Andrea Wong, PhD, VP of scientific and regulatory affairs for the Council for Responsible Nutrition (CRN), told us that CRN was not surprised by the results because vitamin D plays a role in many health functions and vitamin D receptors are all over the body.
"What’s important about this study is that it’s more reflective of the diversity of the American population, with previous studies of vitamin D and cognitive health predominantly focused on white adults."
"For CRN, these data re-emphasize the need to achieve adequate intakes of vitamin D," she said.
Source: JAMA Neurology
Published online, doi:10.1001/jamaneurol.2015.2115
“Vitamin D Status and Rates of Cognitive Decline in a Multiethnic Cohort of Older Adults”
Authors: J.W. Miller, D.J. Harvey, L.A. Beckett, et al.