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Vitamin D is important for bone and muscle health. Vitamin D helps the body absorb calcium and phosphate from food (mostly from milk and dairy). The main role of vitamin D in the body is to make sure there is enough calcium and phosphate to keep the bones healthy and strong. There is also evidence that low vitamin D is linked to other health problems including: a higher risk of bowel cancer, heart disease, high blood pressure, stroke, problems with immunity (how the body fights infections) and autoimmune diseases (including diabetes).
Most vitamin D is made in the skin when the skin is exposed to the sun. This is the best way for our bodies to make vitamin D. Only a few foods (some types of fish) naturally contain vitamin D. It is hard to get enough vitamin D from food alone. Margarine, baby formula and some types of milk have added vitamin D, but most people only get about a quarter (or even less) of their vitamin D needs from food.
Many people with low vitamin D do not have symptoms, but some people with low vitamin D get bone and muscle pain. Very low vitamin D can lead to soft bones, causing rickets in children and osteomalacia in adults. Rickets only occurs when children are growing - if a child has softer bones from low vitamin D, the bones can bend causing 'bow legs' or 'knock knees' as well as other changes. Rickets is more likely in children who also have low dairy intake or in babies that breastfeed for a long time without starting solid foods at the normal age (4-6 months).
Low vitamin D can cause low calcium - this can cause problems with muscle cramps. Low calcium can cause seizures in young babies - if low calcium (or seizures) are found in a baby, they need to come to hospital urgently.
People with low vitamin D (levels below nmol/L) should be treated with vitamin D tablets or mixtures so their levels return to the normal range (over 50 nmol/L)
Vitamin D tablets or mixtures can be low dose (taken daily) or high dose (taken monthly or less often)
People with low vitamin D also need enough calcium in their diet. Most people should aim to have 2-3 serves of dairy each day (1 serve of dairy is equal to 1 glass of milk, 1 tub of yoghurt or 1 slice of cheese)
Low vitamin D is a long term problem. Once low vitamin D is treated the aim is to make sure vitamin D levels stay normal. People who are at risk of low vitamin D need to make sure they spend enough time outside (see below) and should have their levels checked every year. They may need lifelong supplements
For most people, low vitamin D can be prevented by spending time outside.
Babies at risk of low vitamin D (babies who are fully breastfed and have at least one other risk factor) can usually start vitamin D supplements (400 IU daily) from birth to prevent low vitamin D. They should continue this until they are at least one year old.
For more information
Factsheet developed by RCH Immigrant Health. First published December 2009. Updated January 2014.