Elderly people with less vitamin D in their blood may be more likely to develop dementia and Alzheimer’s disease than those with more, according to a new analysis of data from the mid-1990’s.
Severe vitamin D deficiency, and the associated increased risk for dementia, was rare in the study, however. Only four percent of the older people included were “severely deficient” based on their blood samples.
“It is too early to tell whether improving vitamin D levels helps to delay or prevent dementia - clinical trials are now urgently needed,” said the lead researcher from the University of Exeter Medical School in the U.K.
Researchers used data from an existing study of heart disease risk among 1,658 elderly adults. When the study began in 1993, none of the participants had dementia, heart disease or stroke, and all gave blood samples for analysis, which were then stored in a lab.
In 2008, researchers at the University of Washington retested the samples for circulating vitamin D levels.
Most people in the study did have sufficient vitamin D levels in their blood samples, defined as at least 50 nanomoles of the vitamin per liter of blood (nmol/L).
But about 30 percent of people had less than that: 419 people were deficient, with more than 25 nmol/L but less than 50, and 70 people were ‘severely deficient,’ with less than 25 nmol/L. (In Canada, a vitamin D blood level below 76 nmol/L is considered insufficient. )
By 1999, 171 people in the study did develop dementia, including 102 cases of Alzheimer’s disease.
People who had been severely deficient in vitamin D at the start of the study were more than twice as likely to develop dementia in the coming years than people with sufficient levels. Even adults who were moderately deficient in vitamin D had a 53 per cent increased risk of developing dementia of any kind.
The researchers did not test whether taking vitamin D supplements or changing diet plans would have affected dementia risk.
The study findings suggest – but do not prove – vitamin D is important in cognitive function.
Previous studies have suggested that vitamin D supplements may help protect some older adults from fractures or falls.
The change in risk in this study is somewhere between five and 12 percent. Only 10 percent of the participants developed dementia, which increased to 15 and 22 percent of vitamin D deficient and severely deficient people, respectively.
Current research suggests that eating a balanced Mediterranean-style diet rich in oily fish, moderate intensity exercise and the careful management of diabetes, high blood pressure and depression may help reduce dementia risk. Read my eight tips on how to adopt a Mediterranean diet.
Other studies have tied low vitamin D levels to increased risk of any type of disease, but that doesn’t mean that low vitamin D causes those diseases.
Leslie's note: Current vitamin D recommendations range from 600 to 2000 IU per day. In the fall and winter, when the sun isn’t strong enough to produce vitamin D in the skin, Canadians are advised to supplement with 1000 to 2000 IU vitamin D per day.
The safe upper daily limit is 4000 IU per day. Speak to your health care provider about the right vitamin D intake for you.
Source: Neurology, online August 06, 2014.
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