What type are you? Do you take a multivitamin pill everyday, just in case? Or do you trust your body to get all it needs from your diet?
Personally, I fall into the latter category.
Beyond my "things-will-work-out" approach to life, I reassure myself with scientific evidence that most food supplements are unlikely to have much of an effect on health unless you have a specific need (e.g., pregnancy, vegan diet) or a deficiency (e.g., anaemia).
I am currently fairly healthy and eat - most of the time - a balanced diet, so I won't bother with supplements unless my doctor advises otherwise. This suits perfectly my laisser-faire attitude!
Except that it is doesn't work for vitamin D!
This is because vitamin D comes mainly from sunshine, not food (or only very little).
No matter how great my diet might be or how much I may wish to see the sun every day, I am unlikely to get enough of the 'sunshine vitamin' during the winter months.
Even on a bright sunny day, the British winter sun rays are not strong enough for our skin to synthesise enough vitamin D.
And so, currently, most of British population has low or suboptimal levels (NDNS, 2016).
Therefore, in the UK, from October to April, a 10mcg (400IU) vitamin D supplementation is recommended for all adults and children.
(recommendations from the Scientific Advisory Community on Nutrition SACN - the advisory committee to the UK government on nutrition and health related issues)
What is vitamin D useful for?
Bone & Muscles - this is what vitamin D is mostly known for. It plays an essential role in the absorption of calcium and phosphorus and thus keeps bones, muscles and teeth healthy and strong. A deficiency in vitamin D leads to muscle weakness, bone pain, osteoporosis and increase risk of falls and factures in older people.
Immune functions - Vitamin D plays a role in regulating the immune system. There is strong data showing that vitamin D supplementation may reduce the risk of catching flu, for example. And people with upper respiratory tract infections often present low level of vitamin D.
So unsurprisingly, in the last 2 years, so much research focused on vitamin D supplementation as a potential way to prevent Covid-19 or reduce it severity (with fairly inconclusive results so far, it must be said!)
Mental health? Low blood level of vitamin D are prevalent in people with depression which suggests it may help with mental health. Indeed, in a population of people with depression, supplementation with vitamin D has led to an improvement of symptoms. But let's not jump too quickly to conclusion as the current body of evidence is quite small.
Cancer, diabetes, multiple sclerosis, weight, pms, metabolic health, cognitive health? Maybe, maybe not. Vitamin D is being studied for all kind of health aspects and the results are mixed. But vitamin D seems to come into play in many physiological functions.
Take home message: having good blood level of vitamin D is important and may help with many aspects of health and wellbeing. In winter, the best way to ensure adequate levels is through supplementation. Aim for a minimum of 10mcg (400IU) and no more than 100mcg (4,000IU) per day.
For more info on vitamin D, check European Food Information Council (EUFIC)
And for detailed UK recommendations for vitamin D from NICE, check https://www.nice.org.uk/guidance/ph56