- Researchers net new theory on vitamin D and cognitive disorders
- Vitamin D deficiency a risk factor for cognitive decline and dementia
QBI Group Leader Associate Professor Thomas Burne studies brain development and behaviour, and recently published research linking vitamin D deficiency to to a range of cognitive disorders. Here he took questions from people across the world on his team's latest discoveries.
Q: How does vitamin D help the brain?
A: Vitamin D is neuroprotective, regulates the immune system and helps with calcium balance. It is also involved with regulating many genes important for brain function. Although vitamin D is thought of as a vitamin, it acts as a neurosteroid and plays important roles in the brain.
Q: Are there populations that have higher rates of vitamin D deficiency due to seasonal lack of sun exposure or lack of fortified food? And is there a corresponding increase of cognitive disorders in those populations?
A: Great question! There is a clear variation in vitamin D levels around the world depending on latitude and season. There are many epidemiological studies showing an association between season and many brain disorders, including schizophrenia. People with darker skin in colder climates are much more likely to have sub-optimal vitamin D levels than people with lighter skin in colder climates.
Because vitamin D levels will vary between individuals, fortified foods will not be tailored to each person’s requirements. Vitamin D can be sourced from the food we eat, supplements, or from the sun, and we need to get the right balance of each. People with any neuropsychiatric or neurodegenerative disorder will usually have lower vitamin D levels when compared with a similarly aged group of healthy controls.
The evidence suggests that vitamin D deficiency is a consequence of getting ill (people are less likely to go outside, alter their diet, for example). However, our research in mice shows that holding everything constant except for the amount of vitamin D in the diet can have effects on the brain in as little as 20 weeks. Many large clinical trials have looked at supplementing elderly people with vitamin D to prevent falls and fractures, but the data have mostly shown no benefit. It could be that the duration, dose and age when you supplement are important for different outcomes. We need to gather more data to know what works, and what doesn't.
Q: Did you provide the rats with vitamin D again after the 20 weeks of deficiency? And if so, did their ability to remember and learn go back to normal? Maybe vitamin D is a key factor in fighting Alzheimer's?
A: That is a really interesting question. Can we restore the deficits with supplementation? We have not conducted those studies yet in rats or mice. Our hope is that the changes are reversible, but we will have to wait and see the result.
We are cautiously optimistic. We do not have strong evidence from clinical trials that supplementing with vitamin D will cure brain disease. We think that it may slow disease progression, or at least modify symptoms. It may be that one needs to maintain optimal vitamin D levels throughout the lifespan to reduce your risk.
At the end of the day, vitamin D is one of many risk factors and needs to be taken in a broader context (healthy diet, adequate sleep, mental stimulation, etc.). Because vitamin D is relatively safe and cheap, we hope that it may provide some benefit, and hope that it is based on a good understanding of the mechanism of action.
Q: What are your suggestions on naturally obtaining vitamin D, especially in a cold climate? Do you really need to have most of your skin exposed to the sun?
A: In our research we modify vitamin D levels in rodents entirely through the diet. We never expose them to the sun or UVB, and with adequate levels in the food, they have optimal vitamin D (at least in control animals). Curiously rat skin is very efficient at synthesising vitamin D from UVB exposure.
People can obtain vitamin D from multiple sources, including the diet (oily fish), supplements (D2 or D3) or through exposure to the sun (UVB at wavelengths of 290-320 nm). Unfortunately, UVA (320-400 nm) is very damaging to DNA and skin. Although you cannot get too much vitamin D from the sun, you can dramatically increase your risk of skin cancer. So one only needs a relatively small amount of sun exposure to benefit. The problem is that the correct amount depends on the time of day, time of year, amount of skin exposed, skin thickness, skin pigmentation, age, etc., so there is no set time in the sun that would apply to everyone.
Q: Are the side effects caused by a vitamin D deficiency permanent? Does every variant of vitamin D (let’s say 1, 2 or 3) act the same way once absorbed?
A: Vitamin D2 (ergocalciferol) is from plants and Vitamin D3 (cholecalciferol) is from animals. Humans can utilise either source, although D3 is probably more bioavailable than D2. In other animals, such as rats, the bioavailability is different, such that they are equally available.
We believe that some of the effects of low vitamin D are reversible, and others are not. Some of our evidence suggests that it is neuroprotective and one needs optimal levels of vitamin D to reduce the effects of an adverse event. For example, think of a seat belt in a car. If you have a crash and then put the seat belt on it will not do much good, but if you wear your seat belt, although most of the time you will not notice a benefit, in the event of a crash, it will reduce the extent of damage done to your body. It may be that so many studies do not see a benefit of vitamin D because they are focussed on the wrong time, or have the wrong dose, or did not start prior to the insult (or brain injury).
The term vitamin D1 is not used any more. It turns out to be a mixture of D2 and D3, and so those are the two main compounds we refer to.
And one for all you budding students ...
Q: My brain is always malfunctioning at every lecture. Does vitamin D help?
A: In a recent study of undergraduate students, supplementing with vitamin D or placebo did not affect their cognitive outcomes in any meaningful way. It is likely that they were not deficient in vitamin D or their levels were sufficient and they had no other conditions affecting their health. So this would suggest that having optimal vitamin D levels would be ideal, but would be unlikely to affect your performance in a lecture theatre. If you are concerned about your cognition (attention, memory) then you should consult your doctor.
Read more Q&A on this reddit AMA.