What does vitamin D do?
Vitamin D is best known for its essential role in the absorption of calcium to maintain strong bones and teeth, but it has many other important actions, including supporting immunity. Vitamin D:
- Contributes to the normal function of the immune system in adults and children
- Helps with calcium absorption, contributes to the maintenance of bones and teeth
- Contributes to normal muscle function
- Is needed for growth and development of bones in children
Vitamin D deficiency in Australia
In Australia, 23 per cent of people are estimated to have vitamin D deficiency.1 Older adults are particularly at risk, as a result of the age-related decline in the skin's ability to synthesise vitamin D from the sun.2 Anyone who doesn't spend much time outdoors or who covers their skin for religious, cultural or health reasons may also want to consider a supplement.
It is worth noting that in order for your skin to make vitamin D from sunlight, the UV index must be greater than three. As a result, vitamin D deficiency becomes more common during autumn and winter and is most prevalent in the south-eastern states of Victoria (49%), ACT (49%), and Tasmania (43%).3
Even when the sun is shining, many people fail to make enough vitamin D because they sensibly avoid the sun, cover up or use high-SPF sunscreens. Particularly in northern areas of Australia, sun protection is needed all year round, whenever the UV Index is 3 or higher.
Overexposure to UV is never recommended, even if you have a vitamin D deficiency.
Vitamin D foods
Because of this, it's important to get vitamin D from your diet. Vitamin D can be found in useful amounts in:
- Oily fish
- Liver products
- Eggs
- Butter
- Food fortified with vitamin D
This can make it difficult for those following certain dietary regimes (particularly vegetarians and vegans) to get enough, or even those without particular dietary requirements during the colder months.
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Vitamin D benefits and deficiency symptoms
Vitamin D supports many functions in the body, and deficiency can cause problems in anything from immunity to bones and muscles.
Immunity
- Needed for the production of natural defences in the body
- Sufficient vitamin D levels help protect against colds, flu and pneumonia
Vitamin D helps to protect against a number of infections by increasing the production of proteins that are needed for the body's natural antimicrobial defences.4
Studies involving over 19 000 adults found that those with the lowest levels of vitamin D were 36 per cent more likely to develop a common cold than those with high levels, for example.5
The results from 25 clinical trials involving around 11 000 patients from 14 countries show that taking vitamin D supplements reduced the risk of acute respiratory infections such as cold, influenza and pneumonia by 12 per cent, with those who were initially lacking in vitamin D gaining the most benefit.
Because asthma is often triggered by a respiratory infection, taking vitamin D supplements can help to reduce the risk of a severe asthma attack that needs emergency treatment by as much as 61 per cent.
In pregnant women, low vitamin D levels are also associated with bacterial vaginosis (BV), which increases the risk of miscarriage and premature labour. As a result, pregnant women are advised to take a vitamin D supplement.6
Vitamin D deficiency and coronavirus
It has been suggested that one reason why a disproportionate number of people from BAME communities have experienced serious COVID-19 infections may relate to vitamin D status. This is because a higher level of melanin pigment in the skin reduces the ability to synthesise vitamin D on exposure to sunlight.
The National Institute for Healthcare and Excellence (NICE) in the UK recently carried out a 'rapid review' of five published studies to see if vitamin D might offer benefits against the current COVID-19 pandemic. Unfortunately, none of these studies were actual intervention trials of vitamin D supplements for preventing or treating COVID-19, which would have provided the strongest evidence.
Despite this, four of the studies did find an association with those having a lower vitamin D status having an increased risk of subsequently developing COVID-19. However, because four out of the five studies did not adjust for other confounding factors such as obesity and underlying health conditions, NICE concluded that, although there are health benefits associated with vitamin D, there is insufficient evidence to confirm that vitamin D might prevent or treat COVID-19.
Bones
- Needed for the absorption of calcium and phosphorous, essential for strengthening bones
- Deficiency can lead to a lack of bone mineral, particularly in post-menopausal women
Vitamin D is needed for the absorption of calcium and phosphorus, which are required in both adults and children to strengthen bones.
Lack of vitamin D is therefore a risk factor for loss of bone mineral, especially in post-menopausal women, and is therefore also a risk factor for bone fractures resulting from osteoporosis.
The results from 12 studies involving over 42 000 adults show that vitamin D supplements reduced the risk of hip fractures by nine per cent and other non-vertebral fractures by 14 per cent, with higher doses of over 10µg (400 IU) vitamin D per day reducing the risk of non-vertebral bone fractures by at least 20 per cent.7
Muscles
- Has beneficial effects on muscle fibres
- Can reduce the risk of falling due to muscle weakness
Vitamin D also helps to maintain muscles, which in turn helps to reduce the risk of falling due to muscle weakness.
The results from 10 studies involving older adults show that taking a daily vitamin D supplement can reduce falls by 14 per cent compared with placebo.8 This is another reason why vitamin D helps to reduce the risk of bone fractures among men and women aged 60 and older.
Vitamin D3 versus vitamin D2
Vitamin D3 (cholecalciferol) is the form most important for human health, and is the best form to take as a supplement.
The plant form vitamin D2 (ergocalciferol) has a slightly different structure, which makes it less beneficial for maintaining our vitamin D levels.9
Supplements can be taken as tablets or gummies, depending on preference.
How much vitamin D do you need per day?
The nutrient reference value (NRV) for vitamin D is just 5µg (200IU) per day for people aged 19 to 50, 10µg a day for those aged 51 to 70, and 15µg per day for people over 70.
Your ability to make vitamin D in the skin falls as you grow older, and at least halves, or more than halves, between the ages of 20 to 80 years.
In one study, researchers found that people aged 62 to 80 years synthesised four times less natural vitamin D than those aged 20 to 30 years.10
It's therefore a good idea to take a supplement designed for your age. Some experts recommend 25µg for adults aged up to 50 years, and 50µg per day for adults over 50.
Can you take too much vitamin D?
Excessive vitamin D intake can cause side effects due to disturbances in calcium metabolism, such as headache, loss of appetite, nausea, vomiting, diarrhoea or constipation, palpitations and fatigue.
An upper safe intake level of 80µg per day is therefore recommended.11