Vitamin D - explained...
Vitamin D is synthesised when the sun’s rays act on cholesterol in the skin. This is our main source of this important nutrient. It is fat-soluble, acts like a hormone and is stored in the body. Vitamin D helps regulate many body systems including playing a vital role in bone density, the immune system, cognitive function, mental health and many more.
So why are so many people deficient? One reason is that we spend a majority of our time indoors; another, is geographical location. The further you are from the equator the less able your skin is to synthesise vitamin D. This is particularly so in the northern hemisphere between October and April. In addition, people of darker skin colour and the elderly tend to synthesise less. Other reasons are if one is fully covered when out or use sun block all of the time. Whilst excess exposure to the sun is damaging, short-term exposure is necessary to synthesise vitamin D.
Food sources of vitamin D are oily fish such as salmon, mackerel, anchovies, eggs, dairy and mushrooms if they have been exposed to UV rays.
Ideally, we should check our Vitamin D levels through a blood test which can be arranged through your doctor or, if in the UK, by ordering a home test kit online at vitamindtest.org.uk. The NHS in the UK recommends supplementing 400 IU of vitamin D daily for an adult through the winter months but if your level is low, 1000 IU or more per day may be needed.
Different countries have different optimal levels for vitamin D. In France, it is considered to be between 30 - 60 ng/mL (or 75 to 150 nmol/L).