What does a vitamin D deficiency do to your brain?
A vitamin D deficiency is associated with a higher risk of cognitive decline and dementia, but whether correcting it through supplements genuinely protects the brain has not yet been proven. If you are below the threshold, discuss it with your GP.
Vitamin D is active in the brain, and this has been known for longer than many people realise. Brain tissue contains receptors for vitamin D, both in the developing brain and in the adult brain. Through those receptors, vitamin D influences the transmission of signals between nerve cells, the production of antioxidants, and the health of the energy centres within cells. A deficiency disrupts all of these processes at the same time.
The link between low vitamin D levels and cognitive decline has been found in multiple studies. In cases of severe deficiency, a blood level below 25 nmol/L, the risk of cognitive impairment was up to four times higher than in people with a sufficient level above 75 nmol/L. Something similar applies to Alzheimer's disease: low blood levels are associated with a higher likelihood of the condition, and the active form of vitamin D appears, in cell and animal research, to be capable of helping to clear the characteristic protein accumulations (amyloid plaques).
Low vitamin D levels are also found more frequently in other brain conditions, including Parkinson's disease, multiple sclerosis, and schizophrenia. The findings here are contradictory, however. There is some indication that vitamin D is also involved in the stability of the protective sheaths surrounding nerve cells, which may play a role in schizophrenia. This remains a hypothesis, based on animal and laboratory research.
The crucial caveat: almost all of these associations were found in studies in which people were followed over time without anyone being assigned a supplement. Whether raising levels through supplementation actually protects the brain has not yet been demonstrated. The authors of the review studies are clear about this themselves: most studies are observational, intervention research yields contradictory outcomes, and the findings must be interpreted with caution. The protective mechanisms are biologically plausible and well documented in cell and animal models, but robust clinical confirmation in humans is still lacking.
This answer is based on multiple summary reviews of the available research, and does not include large randomised studies capable of establishing cause and effect. The authors themselves state this explicitly: most studies are observational, few intervention studies have been conducted, and those that exist yield contradictory results. They write explicitly that the findings are controversial and must be interpreted with caution. The mechanistic evidence (from cell and animal research) is stronger than the clinical evidence in humans.
Does years of insufficient sleep damage your brain?
Years of insufficient sleep damages the brain through multiple pathways at once, and some of that damage appears difficult or impossible to reverse. Make sure you consistently get enough sleep, and have sleep apnoea treated if you have symptoms of it.
What does air pollution do to your brain in the long term?
Long-term exposure to air pollution, and fine particulate matter in particular, is associated with an increased risk of dementia and faster memory decline. The associations have been demonstrated in multiple human studies, but a direct cause-and-effect relationship has not yet been conclusively proven.
What does high cholesterol do to your brain as you age?
High cholesterol in middle age likely increases the risk of dementia, but at older ages the relationship is less clear and cholesterol-lowering drugs have not been proven effective for the brain. Stable cholesterol appears wiser than strongly fluctuating values; discuss your risk profile with your doctor if you are concerned.
What does excess weight do to your brain in the long run?
Excess weight harms your brain in multiple ways at once: less brain tissue, weaker connections and a higher risk of dementia. Exercise combined with diet appears to be able to partly reverse this, so losing weight is good for your brain too.
Can a vitamin D deficiency affect your hormones?
A vitamin D deficiency disrupts hormone levels, primarily through a rise in parathyroid hormone PTH, which affects your bones, muscles, and possibly your heart. The effect on sex hormones such as testosterone appears limited, but this has been too little studied to allow firm conclusions.
What does a vitamin D deficiency do to your DNA?
A vitamin D deficiency is associated with greater DNA damage, especially in people with an additional risk factor. Make sure your vitamin D level is adequate, but if you are unsure about supplementation, consult your general practitioner.