What vitamin D does
Vitamin D helps the body regulate calcium and phosphate, which are important for bones, teeth and muscles. The body can make vitamin D when sunlight reaches the skin. Food sources include oily fish, egg yolks and some fortified foods.
Why the seasons matter
NHS advice varies with the season and how much sunlight you get. Its vitamin D guide explains who may need vitamin D throughout the year and gives age-specific guidance.
Read amounts with the units attached
Vitamin D is often listed in micrograms, written as µg. If you already take a supplement, make a list of the ingredients and amounts, including any multivitamins, before asking a pharmacist about your total intake.