A sunny day can make you feel happy, but it may also help retain some of your cognitive powers. New research suggests that vitamin D, often obtained through sun exposure, might be good for our brains, particularly those of women.

The observational study, published in Maturitas, investigated the association between midlife vitamin D and cognition in Australian women over 10 years. It used data involving 252 participants aged 55-67 from the Women's Healthy Ageing Project.

The study found that sufficient midlife vitamin D levels, which works out to be more than 25 nanomoles per litre (25nmol/L), were associated with improved aspects of executive function in ageing. It also identified a potential midlife window where ideal levels of vitamin D could protect against some types of cognitive decline.

Lead author Dr Alicia Goodwill, an Honorary Fellow at the University of Melbourne's Department of Medicine (Royal Melbourne Hospital), says executive function relates to a number of processes and cognitive control functions.

"These include attention, cognitive inhibition, cognitive flexibility and working memory," she says. "In this study, the main processes of executive function assessed were cognitive flexibility and attention."

The researchers found that although there was some evidence to suggest a more pronounced effect of vitamin D status on cognitive processes in women, until now no study had followed this association from midlife to late-life.

"Women (age range 55-67 years) with vitamin D levels above 25nmol/L maintained better executive functioning in late-life, in particular improved cognitive flexibility, attention and psychomotor speed," it found.

Memory did not appear to be affected by vitamin D levels in this study, but Dr Goodwill says that declines in memory performance often occur later than other cognitive domains, and may not be clinically detectable until women reach their seventies.

She says the findings are another potential piece in a research puzzle that has identified dementia risk factors such as type 2 diabetes, hypertension, obesity, smoking, depression, physical inactivity, and low cognitive stimulation or low education.

"It's one lifestyle factor in a holistic view of protecting our brains as they age," she says of vitamin D. "We're not saying it's a magic bullet or the magic sunshine. It's one potential factor."

This latest study involved the Australian Catholic University's Institute for Health and Ageing, the University of Melbourne's Department of Medicine and Department of Psychiatry, the Australian Healthy Ageing Organisation and Royal Melbourne Hospital.

Dr Goodwill says the emerging data is timely given modern lifestyles that involve long hours indoors at desks, TV time and less active transport. She says people should ensure they get enough vitamin D and that combining small amounts of sunshine with light exercise such as a walk, gardening or putting out the washing is an effective way to obtain sufficient amounts of vitamin D.

"Exercising outdoors is a great way to encourage people to get enough vitamin D, and given exercise also has positive effects for our brain health, this is an added benefit," she says.

"Of course, the exact amount of sun exposure required varies across individuals, with factors such as increasing age and darker skin pigmentation influencing the effectiveness to synthesise and produce vitamin D."

Dr Goodwill says the 'slip slop slap' message is still important and the need for sun exposure for vitamin D synthesis needs to be carefully balanced with the risk of sunburn and skin cancers. Supplements can help replete levels in those who are vitamin D deficient.

However Dr Goodwill, who is also a researcher with the Australian Catholic University's Institute for Health and Ageing, says there is not yet enough strong evidence that supplementation improves cognitive performance, or prevents cognitive decline or dementia.

Senior author and University of Melbourne Neurologist Professor Cassandra Szoeke says the latest results suggest optimal vitamin D in midlife may be an important target to slow cognitive ageing. But she says the only way to confirm such a cognitive benefit would be a randomised controlled trial where half of a vitamin D deficient cohort was administered vitamin D and the other half not was not, to see which had better outcomes.

"Given that it takes approximately 20-30 years to progress from normal cognition to dementia, such trials are not feasible or ethical, therefore we rely on high-quality observational evidence to guide practice in this field," she says.

Professor Szoeke adds that improving our cognition appears to involve a number of factors. "The earlier we are aware and modify lifestyle factors that are linked to cognitive health, the better and it is never too late to make positive changes to our health."

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