Vitamin D can be found in certain food sources, but the absorption can be limited, and our diet alone may not deliver a high enough level of the nutrient.

From sun: The sun is the most significant source of vitamin D. The skin produces vitamin D3 (cholecalciferol) when exposed to UVB radiation from sunlight. Just 10-15 minutes of sun exposure 2-3 times a week is enough to produce sufficient vitamin D levels in most people. However, sunscreen with SPF 30 can reduce vitamin D production by up to 95%. During the winter months in the UK, UVB exposure is limited with or without sunscreen.

From food: Some foods are fortified with vitamin D, such as milk, orange juice, and cereals. Fatty fish such as salmon, tuna, sardines, herring, and mackerel are good sources of vitamin D, and egg yolks also contain small amounts of vitamin D. However, animals need sunlight to produce vitamin D, which means intensive farming practices can limit the availability of good quality food sources.

Vitamin D is fat-soluble, which means that it is easier to absorb when deliver in a form that includes fat. Full-fat products fortified with vitamin D are more easily absorbed than low-fat products.

If you are vegan or vegetarian, animal-based products are off-limits, and you can find it tricky to get enough vitamin D in your diet, which means supplementing your intake is crucial.

Many of our patients have chronic health issues, such as celiac disease or Crohn’s disease, which cause issues with the absorption of vitamins. Liver disorders may also have an effect on the availability of vitamin D as the nutrient is stored in the liver, which can lead to problems in converting it to the active form of vitamin D.

There are a few other reasons why someone might be deficient in vitamin D:

• Obesity
• They don’t spend enough time outdoors, including those who are bed bound
• They always wear sunscreen when outdoors which interferes with vitamin D production
• They have a darker skin tone, which limits the skin’s ability to produce vitamin D from sunlight exposure. People with darker skin tones may only produce a sixth of the amount of vitamin D from sun exposure than those with lighter skins
• Age plays a factor – absorption often decreases as you get older, which is significant in those over 60

Vitamin D helps to maintain bone density (preventing osteoporosis) and bone health by aiding the absorption of calcium and phosphate in the body. The vitamin supports the immune system and regulates the activity of over 200 different genes.

Vitamin D also works to reduce inflammation, protect and support the heart and brain, modulate cell growth, and may relieve arthritis symptoms. It is possible it also protects your body from respiratory infections.