It has long been known that vitamin D – often referred to as the “sunshine vitamin” – is one of the most essential vitamins for our overall health because it regulates calcium in the body and maintains the integrity of bones. Over the past decade, though, our understanding of this vitamin’s importance has expanded in response to a flood of research suggesting an association between vitamin D deficiency and a wide range of physical health problems such as cancer, cardiovascular disease, diabetes, and autoimmune diseases.
Vitamin D deficiency has also been linked with diseases related to mental health and brain function, including depression, schizophrenia, cognitive impairment, and dementia. These interesting findings have been shared widely in the news, and, in response, sales of vitamin D supplements have skyrocketed as people try to prevent or treat health conditions by boosting their intake.
However, the public’s enthusiasm for vitamin D supplementation may not be justified by the evidence collected to date. Yes, associations have been discovered between vitamin D deficiency and many illnesses (meaning, researchers have found that individuals who are deficient in vitamin D are more likely to have certain illnesses than those with sufficient vitamin D levels), but such associations do not prove causality. In other words, these research findings do not make it clear if vitamin D deficiency plays a role in causing the various illnesses, or if having one of the illnesses plays a role in causing vitamin D deficiency.
Alternatively, it is possible that a separate variable could be at the root of both the vitamin D deficiency and the illnesses.In this article, we’ll examine some of the latest research findings about vitamin D’s impact specifically on brain health. Is Vitamin D Linked to Dementia?
The research findings about the association between vitamin D deficiency and dementia have varied from study to study. This has led many researchers to consolidate and analyze evidence collected by others, in an attempt to reach a definitive conclusion. This type of consolidated research is called a “systematic review” or “meta-analysis.” Below are summaries of two recent examples of this type of research:
- Researchers from China Medical University conducted a meta-analysis that analyzed the collective findings of ten studies, published between 2011 and 2017, which examined the relationship between 25-hydroxyvitamin D levels and dementia and Alzheimer’s disease. 25-hydroxyvitamin D (25(OH)D) is the form that vitamin D takes after being processed in the liver. It can be measured in the blood, and is considered a good indication of the amount of vitamin D in a person’s body.
When the data from the studies – involving more than 28,000 participants – was pooled and analyzed, a significant inverse relationship was found. For every 10 nmol/L increase in 25(OH)D level, the researchers found the risk of dementia decreased by 5% and the risk of Alzheimer’s disease decreased by 7%. (Note that all of the studies were used in calculating the dementia risk, but only some of the studies looked specifically at Alzheimer’s disease – a subtype of dementia – so the Alzheimer’s risk percentage is based on a smaller set of data.) The researchers – Hanze Chen and colleagues – concluded that maintaining adequate 25(OH)D levels may lower risk of dementia and Alzheimer’s disease. These findings were published in November 2018 in Frontiers in Aging Neuroscience.
- A research team from Canada and Australia undertook an assessment of the quality of systematic reviews that had been conducted up to June 2017 about the association between vitamin D and dementia. “Out of six meta-analyses we reviewed on the association between low vitamin D levels in the blood and dementia risk, five showed a positive association,” said Dr. Fariba Aghajafari, an associate professor at University of Calgary and lead author of the study. These researchers concluded that there may be an association between vitamin D status and dementia risk, but the strength of evidence collected to date is low.
“Although the results of the reviews we assessed suggested a positive association between lower vitamin D levels and the development of dementia, our assessment of the quality of that research suggests that the findings should be interpreted with caution,” continued Dr. Aghajafari. “More research, using well-designed methodology, is needed to fully understand the nature of the relationship between vitamin D status and dementia risk.”
This research was published in June 2018 in BJPsych Open.Is Vitamin D Neuroprotective?It seems likely that there is a relationship of some kind between vitamin D status and dementia. Accordingly, could increasing vitamin D levels provide some kind of a boost to brain health? This is a question that researchers have also explored extensively in studies involving both animal and human subjects.Australian researchers conducted a systematic review – published in July 2018 in Nutritional Neuroscience – of over 70 studies that examined the role of vitamin D across multiple neurodegenerative diseases, including multiple sclerosis (MS), Parkinson’s disease, and Alzheimer’s disease.
The evidence they reviewed, from research conducted up to 2016, did not suggest that vitamin D is a protective agent for the brain.“Our analysis of the research showed that the link between vitamin D and brain disorders is likely associative,” explained Dr. Mark Hutchinson, a professor at the University of Adelaide and one of the authors of the study. “It’s not likely a directly causal relationship.”
Accordingly, the researchers concluded that strong recommendations cannot be made about the therapeutic benefits of dietary vitamin D supplementation in neurodegenerative disease, based on the evidence to date.
Perhaps Sun Exposure is Key
The body produces most of its vitamin D in response to ultraviolent B (UVB) radiation from sun exposure on the skin. It can also be obtained from a few foods such as oily fish and fortified foods (e.g. milk and orange juice), as well as from vitamin D supplements. It may be that sunlight creates other “x-factors” that are neuroprotective, separate from the sun’s contribution to vitamin D levels.Dr. Hutchinson and his colleagues considered this possibility and concluded that it has merit. “Our research indicated that it’s possible sensible and safe sun exposure is good for the brain in ways we have yet to identify, ways that may not have anything to do with vitamin D, meaning we cannot yet put sunlight into a supplement tablet,” he explained. “Some early studies suggest that UV exposure could have a positive impact on some neurological disorders such as MS, but more research is necessary to fully understand what’s happening.”
Sun Exposure Guidelines for Vitamin D
Because most of our vitamin D comes from sun exposure, and sun exposure may have additional health benefits beyond being a source of this essential vitamin, it appears that we may benefit from spending some time outdoors with exposed, bare skin (i.e. without sunscreen).But how can one maximize the benefits of sun exposure while minimizing the risk of skin cancer? Recommendations about safe sun exposure vary widely, with some experts advocating for zero sun exposure (i.e. getting all of your vitamin D intake from food and supplements) and others recognizing the need for some sunshine.The amount of time that each person needs to spend outdoors in order to achieve a sufficient vitamin D level and enjoy any other health benefits of sun varies based on a number of variables, including season, latitude, time of day, amount of exposed skin, age, weight, and skin colour. Consequently, there is no single recommendation for safe, healthy sun exposure that is suitable for all.
However, a mobile application called “dminder” (http://dminder.ontometrics.com/) has been created to help individuals determine how much sun exposure is enough on any given day, factoring in the user’s unique variables.Although the exact amount of sun exposure that is safe and ideal varies, the amount of time required is minimal for most individuals. For example, the National Health Service in the U.K. suggests that most people can produce enough vitamin D from being out in the sun daily for short periods with their forearms, hands, or lower legs uncovered and without sunscreen from late March or early April to the end of September, especially between the hours of 11:00 a.m. and 3:00 p.m. There are parts of the world where there are no UVB rays in the colder months. If you live in one of these places, your body may make and store enough vitamin D in the warmer months to get you through the colder months. It is important, though, to check with the country-specific recommendations about vitamin D levels.
How Much Vitamin D is Sufficient?
There is a lack of consensus in the medical community about what constitutes a “sufficient” level of 25(OH)D. Some consider levels of 20 ng/mL (50 nmol/L) sufficient, and levels below that deficient. Yet, others, including the Vitamin D Council, suggest 40 ng/ml (100 nmol/L) should be the cut-off between deficient and sufficient.
How Common is Vitamin D Deficiency?
It is estimated that 1 billion people worldwide are deficient in vitamin D. Older adults are more likely than other age groups to have vitamin D deficiency for several reasons, including low dietary intake, inadequate sun exposure, and decreased ability of the skin to synthesize vitamin D from the sun.
Much More to Learn:
Although researchers are discovering interesting findings about vitamin D and sunshine, much more research is needed. In the meantime, the following are some key messages from the research to date:
- Vitamin D is essential for health – certainly one’s bone health, and possibly other areas of physical, as well as mental, health (including brain health). Any vitamin D deficiencies should be addressed through either safe exposure to sunlight and/or increased dietary intake of vitamin D (food and/or supplements).
- Safe exposure to sunlight is key – be sure to take steps to avoid getting too much sun. For instance, seek shade, cover up, and use sunscreen for much (but not all) of your time outdoors.
- More is not necessarily better – if you are taking vitamin D supplements, taking more than is necessary to reach a “sufficient” level may not provide any therapeutic benefit, particularly for brain health. Nevertheless, vitamin D supplements are fairly inexpensive and they are safe to take in recommended dosages.
Article by Women’s Brain Health Initiative
Source: MIND OVER MATTER V9