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We all need vitamin D as it helps your body absorb calcium and phosphate from the foods you eat to give you strong and healthy bones, teeth and muscles.
Vitamin D also plays a role in the growth of your cells, the functioning of your immune system and in reducing inflammation.
But vitamin D deficiency is common, affecting 1 in 5 people in countries such as the UK. Being deficient increases your risk of developing conditions that weaken your bones, like rickets or osteomalacia.
There are steps you can take, however, to make sure you get enough.
Guidance around the amount of vitamin D you need varies slightly by country. The UK’s National Health Service recommends that all adults and children over 1 year get 10 micrograms per day -- this is 1 hundredth of a milligram.
The National Institutes of Health (NIH) in the US recommend 15 micrograms per day.
Your body makes vitamin D when your skin is directly exposed to the sun, making sunlight the main source of the nutrient for many people worldwide. But you can also get vitamin D from certain foods and by taking supplements.
During spring and summer months, or in countries that have sunshine for most of the year, most people will get enough vitamin D from direct sunlight.
But cloudy days, shade and having darker skin will reduce the amount of it your body makes. Higher levels of the pigment melanin in darker skin cause it to produce less vitamin D.
Also, if you sit indoors by a window your body won’t make vitamin D, as the ultraviolet rays from the sun that it needs to do this can’t get through the glass.
You should, however, take care when out in the sun by wearing sunscreen and protective clothes to reduce your risk of skin cancer.
Certain foods contain vitamin D, with fatty fish such as salmon, tuna, herring and mackerel being the best sources as these have over 10 micrograms per portion.
You can also get a small amount in red meat, liver, egg yolks and cheese.
Some foods are also fortified with vitamin D, such as breakfast cereals, milk and spreads. You should check the packaging for more information as this will vary by country.
Advice around supplements varies by country. The UK’s Department of Health and Social Care advises that people who spend a lot of time indoors, or who wear clothes that cover up their skin most of the time, should take a daily supplement of 10 micrograms of vitamin D.
In seasonal countries it’s advised that everyone take supplements during the autumn and winter months. It’s unlikely you’ll get enough vitamin D during that time through your diet alone given the lower amounts of sunlight.
If you have darker skin and live in a seasonal or cold country, you may want to take supplements throughout the year. People over 70 should also consider this as skin becomes less efficient at creating vitamin D as you age.
Other groups at greater risk of deficiency include people with disorders that mean their bodies don’t handle fat properly, such as inflammatory bowel disease (IBS), Crohn’s disease and coeliac disease, according to the NIH. This is because vitamin D needs fat in order to be absorbed.
Obese people are also at risk of deficiency because their fat may bind to some of the vitamin D and prevent it from being absorbed properly.
When your vitamin D levels are low you may feel tired and weak and experience bone or muscle pain.
Being deficient over a long period of time can lead to osteomalacia in adults, where your bones become softened, causing bone pain and muscle weakness. This is a result of your body being unable to absorb enough calcium.
In children, deficiency can cause rickets, where bones become soft and bend, causing pain, poor growth and bone deformities.
Studies have also linked vitamin D deficiency to an increased risk of bone disorders, such as osteoporosis. Current research is exploring links with certain cancers as well as diabetes and hypertension.
Mental health conditions such as depression, low mood and schizophrenia may also be related to low levels of vitamin D.
Experts recently suggested that vitamin D might also play a role in protecting you against coronavirus and other respiratory infections, or treating them if you do become ill.
But a new set of studies, including 1 by the National Institute for Health and Care Excellence (NICE) in the UK, concluded that there’s not enough evidence of this protective effect. Previous studies had a similar result.
It is possible to have too much vitamin D as your body only needs a small amount each day. But this is usually caused by taking too many supplements.
An overdose of supplements can lead to your body absorbing too much calcium, causing it to build up and weaken your bones as well as damage your heart and kidney -- a condition called hypercalcaemia.
Excess vitamin D can also cause nausea, vomiting, poor appetite, weight loss and constipation.
High levels of calcium in the blood -- due to a lot of vitamin D -- can also cause confusion, disorientation and heart rhythm problems.
But it’s important to note this will usually be due to taking too many supplements, so taking the right amount will correct this. If you’re concerned you should speak to a doctor.
There’s no risk of producing too much vitamin D from the sun as your body regulates the amount it produces.
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.