Question: The “Nutrition Bite” about vitamin D and dementia (April 1) was worrying. Does the study imply that all people over 70 should take a vitamin D supplement to prevent dementia or only people in the Northern Hemisphere? If it is that effective, why is it not in the general advice list, like exercise and socialising, to avoid or delay dementia?
Answer: About 70,000 New Zealanders are living with dementia today, but that number is predicted to grow to 170,000 by 2050 as our population steadily ages. And the effects of dementia are widely felt, with Alzheimers New Zealand’s 2021 Dementia Economic Impact Report estimating that partners of people living with dementia provide over one million hours of unpaid care each week. That burden can cause stress, depression and a range of other health complications for carers. Undoubtedly, then, maintaining our cognitive health in later life is a priority, so what should we do?
The brief about vitamin D and dementia referred to a study published in the journal Alzheimer’s & Dementia: Diagnosis, Assessment & Disease Monitoring. It reviewed observational data from more than 12,000 older adults tracked in the US National Alzheimer’s Coordinating Centre database. It found a 40% lower incidence of dementia among individuals taking any form of vitamin D supplement.
But before we all rush out to buy vitamin D supplements, let’s delve deeper into what these findings mean and what the researchers recommend.
For starters, this study was observational, and so does not provide as reliable information on causal relationships as a randomised clinical trial. So, although it can say researchers found an association between people taking vitamin D supplements and a lower risk of dementia, it cannot definitively say the supplement caused the lower dementia risk. Similarly, we cannot say that male pattern baldness increases the risk of cardiovascular disease. Instead, men have a higher risk of cardiovascular disease, and they also happen to develop male pattern baldness with age, but the two are not causally related.
However, there are plausible reasons to believe increasing vitamin D intake may reduce dementia risk. For example, vitamin D participates in the clearance of amyloid beta plaques, a characteristic of Alzheimer’s disease. It may also protect against tau hyperphosphorylation, another aspect of the disease that affects brain function. Moreover, several other extensive observational studies have shown that low vitamin D status precedes the emergence of dementia, not vice versa, adding to the evidence that low status may cause increased dementia risk.
However, we still need more evidence, says study co-author Dr Byron Creese, of the University of Exeter. “The link with vitamin D in this study suggests that taking vitamin D supplements may be beneficial in preventing or delaying dementia, but we now need clinical trials to confirm whether this is really the case. The ongoing VitaMIND study at the University of Exeter is exploring this issue further by randomly assigning participants to take either vitamin D or a placebo and examining changes in memory and thinking tests over time.”
So, more time and research are needed to confirm the role of supplementary vitamin D in dementia prevention.
Meantime, adopting a healthy diet and active lifestyle may be our best defence against cognitive decline in older age, according to findings from a clinical trial published in the Lancet in 2015. Finnish researchers ran a two-year clinical trial of a lifestyle intervention involving more than 1200 older adults at risk of cognitive impairment or Alzheimer’s disease. The participants were randomly assigned to receive either standard healthcare or healthcare plus guidance on nutrition and physical exercise, cognitive training, social activities and management of cardiovascular health.
After two years, the group following the lifestyle intervention performed significantly better on memory, executive function (eg, planning, judgment and problem-solving) tests, and cognitive processing speed, suggesting a healthier, active lifestyle and diet delays cognitive decline. So, with or without vitamin D supplements, we can gain much from a healthy, active lifestyle.
