Please note: Information, evidence and advice relating to COVID-19 is constantly changing. The information in this article was correct at the time of writing.
During the COVID-19 pandemic, many Australians have been spending more time indoors than usual, because of the restrictions in place to limit transmission of the virus.
In addition to reducing the spread of COVID-19, restrictions have also helped slow down the spread of many common infectious diseases including influenza (flu), measles and chicken pox. However, there are health-related drawbacks to spending less time outside.
International health authorities have been concerned that reduced exposure to sunlight has left some people vulnerable to a vitamin D deficiency.
Vitamin D is important for bone, muscle and dental health. Some recent reports have also suggested that vitamin D levels may influence risk of COVID-19 infection and severity.
Read on to find out more about vitamin D.
What is vitamin D?
Vitamin D is an essential vitamin that helps to regulate calcium in your body, which is why it’s so important for bone health.
The source of most vitamins needed by humans come from the foods we eat. Vitamin D is different to other vitamins because it is produced when our skin is exposed to the sun (which is why it is sometime called the ‘sunshine’ vitamin). Only 10% of our vitamin D supply comes from food, like egg yolks and mushrooms, or from fish that have a lot of fatty tissue such as salmon and herring.
Vitamin D is unique in the way it’s produced and used in our bodies, and because of the role it plays in balancing calcium levels it’s sometimes thought to be more like a hormone than a vitamin.
There are different forms of vitamin D, which is why it can have different names. Health professionals may refer to it as calcitriol (1,25-dihydroxyvitamin D), ergocalciferol (vitamin D2), cholecalciferol (vitamin D3), or calcifediol (25-hydroxyvitamin D or 25(OH)D).
What does vitamin D do?
Vitamin D has an important role in helping the body absorb calcium. Calcium helps to keep our bones, muscles and teeth healthy and strong.
Throughout pregnancy, having good vitamin D levels is important for a baby’s bone development.
There is also some evidence that vitamin D plays a role in our immune responses, which researchers are trying to understand.
One clue that suggests a link between vitamin D and immunity is the presence of vitamin D receptors on the surface of human immune cells. Receptors are like a lock in a door that can only be turned with the ‘right key’. Opening the lock causes actions to occur that can change how a cell behaves. Some researchers believe that having vitamin D receptors on almost all of our immune cells means that vitamin D is able to ‘unlock’ a response in those cells and so influence our immune system activities.
Can vitamin D supplements protect me from COVID-19 infection or prevent severe complications?
Having enough vitamin D is important for your overall wellbeing, and looking after your health is crucial during this time. However, taking supplements (including vitamin D) to prevent COVID-19 infection is not supported by any clinical evidence.
The best ways to avoid infection with the SARS-CoV-2 virus are to get vaccinated if you are able/eligible, practice good hand hygiene and physical distancing, and to follow restrictions and recommendations from the federal and state or territory departments of health.
Some international studies have reported that people who died after being diagnosed with COVID-19 tended to have low levels of vitamin D. Many of those people were older and had age-related health issues or other conditions before they contracted coronavirus. A review of available data by the National Institute of Clinical Excellence in the UK has concluded that age and health status – not vitamin D levels – made these people more vulnerable to poor health outcomes after being infected with COVID-19.
One group of research scientists from the UK said that it’s 'plausible' a person with low levels of vitamin D could be more susceptible to a COVID-19 infection, because of vitamin D’s role in our immune system, but a direct link has not been established.
There is currently no evidence to demonstrate that vitamin D supplements can protect people with COVID-19 from more serious health complications. Clinical trials are underway to examine the topic further.
What happens if vitamin D levels in the body are too low?
It is well established that low levels of vitamin D can contribute to bones becoming more fragile and prone to breaking due to loss of bone mineral density. In mild cases, this is known as osteopenia. In more severe cases, this is known as osteoporosis, which occurs when your bones lose calcium and other minerals at a rate that’s too fast for your body to replace.
Vitamin D deficiency in older people is also linked to poorer muscle strength and increased risk of falls.
In children, low vitamin D could lead to weak and soft bones that don’t form the way they should. This disease is called rickets. In adults, a softening of the bones is called osteomalacia.
In addition to having adequate levels of vitamin D and calcium, exercise is another important element required to reduce risk of osteoporosis and falls.
How do I get vitamin D?
The best natural source of vitamin D is when skin is exposed to the sun’s UVB rays. However, balancing sun safety and vitamin D requirements can be tricky, as UVB rays cause sunburn and increase skin cancer risk. It’s good to check the UV index before you go outside to determine the level of sun protection you need. In Australia you should not go outside without sun protection if the UV level is above 3. Examples of sun protection can include using sunscreen, or wearing a hat, sunglasses or clothing that covers your skin.
You can find the UV level by going to the Bureau of Meteorology’s website and clicking on the weather forecast for your location – the bottom of each day’s listing will contain details about the UV level. The free SunSmart app can also provide information relevant to your current location.
In summer, people with fair skin can obtain adequate vitamin D levels by spending 5–10 minutes in the sun between 10 am and 2 pm. In winter, you might need to spend up to half an hour outdoors during the middle of the day, if you live in southern Australian states or territories.
For those with darker skin it can be more difficult to obtain adequate vitamin D from the sun – about 3–6 times more sun exposure is needed.
As described previously, small amounts of vitamin D can also be obtained from food such as oily fish and eggs, but food can only make up a small portion of your daily requirement.
Some people may not be able to spend enough time in the sun or may not be able to produce vitamin D easily. Health professionals may recommend vitamin D supplements after considering individual circumstances, including whether vitamin D deficiency is present and how severe it is.
What level of vitamin D should I have?
When discussing vitamin D levels, health professionals will refer to a type of vitamin D known as calcifediol – which is also called 25-hydroxyvitamin D and shortened to 25(OH)D.
In Australia, blood serum levels of 25(OH)D that are equal or higher than 50 nmol/L are considered adequate.
How do I know if I have a vitamin D deficiency?
In Australia, 23% of the population are estimated to be vitamin D-deficient.
Some people in the population are more likely to have low vitamin D levels due to physical, medical or environmental factors. They include:
- people with a history of skin cancer or who are at high risk of skin cancer
- people who wear concealing clothing
- people who have naturally dark skin
- people who spend long hours indoors due to their occupation or their health conditions, including those who are housebound or living in institutions, such as aged care facilities
- older adults
- people with certain medical conditions such as obesity or malabsorption
- young children born to a person who was vitamin D-deficient while pregnant.
I think I’m deficient in vitamin D – what should I do next?
If you belong to a group who are more likely to be deficient in vitamin D, you should talk with your health professional about the next steps.
They may direct you towards a blood test to check your levels or towards vitamin D supplements.
If you have no reason to believe that you might be vitamin D-deficient, supplements will not improve your health outcomes.
Taking extremely high doses of vitamin D supplements can lead to high amounts of calcium in the blood – a condition called hypercalcemia. Over time this can cause severe kidney and bone damage.