Vitamin D deficiency

Are you getting enough vitamin D?
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01 .Who's missing out?


Studies among the general population in Australia have found that 23-49% of people suffer mild vitamin D deficiencies. Another 7-10% suffer from moderate to severe deficiencies. 

This article explains:

For more information about Health conditions, see General health.

What is vitamin D?

Vitamin D is primarily known for its role in bone health. It helps with the absorption of calcium and phosphate, reduces calcium loss from bones and is needed for bone growth and remodelling. 

There are suggestions that it also plays an important role in other aspects of human health, especially immunity and infection control, and recent research on tuberculosis bacteria has shed light on the critical role vitamin D plays in the function of T-cells, which are white blood cells that fight infection in the body. 

It’s also linked with fighting flu and other respiratory infections due to its role in the production of infection-fighting amino acids (antimicrobial peptides).

Our main source of vitamin D comes from exposure to sunlight. A steroid in the skin, called 7-dehydrocholesterol (7-DHC), is converted to vitamin D3 – called cholecalciferol – through the action of solar UVB radiation. 

Other minor sources of vitamin D3 are fatty fish, eggs, meat and fortified foods. Vitamin D2 (ergocalciferol) comes from fungi, and may be used in supplements.

Risk factors

Some people are at higher risk of deficiency including:

  • People who are housebound, or living in a long-term care facility, such as a nursing home, or shift workers who sleep through the day. Studies have found that up to 77% of aged care residents are deficient.
  • People with naturally dark skin Dark skin has a sun protection factor of up to 15 – so, the equivalent of wearing SPF15 sunscreen. In equatorial regions, where there’s plenty of sun, this isn’t such a problem, but dark-skinned people living further north or south may need supplements.
  • People who cover themselves for religious or cultural reasons, or due to increased risk of skin cancer or other skin conditions. 
  • People who live in southern parts of Australia have a higher risk of deficiency than those in the north, although people in the north may also be at risk due to skin cancer prevention measures.
  • Obese people Vitamin D is readily taken up by fat cells, and it’s believed obese people have vitamin D stored in body fat instead of doing what it should do elsewhere in the body. 
  • Elderly people have lower concentrations of the 7-DHC in the skin, and need larger amounts of sun than younger people. To avoid skin damage, though, supplements are a safer option.
  • People with certain diseases or conditions suffer from reduced vitamin D absorption and/or synthesis, including Crohn’s disease, coeliac disease, inflammatory bowel disease, cystic fibrosis, chronic pancreatitis, and kidney or liver disease. 
  • Certain medications also contribute to vitamin D deficiency, including rifampicin (an antibiotic) and anticonvulsants.

Bones, blood pressure and more

The most common results of vitamin D deficiency are: 

  • Rickets (softening of the bones during childhood)
  • Osteomalacia (softening of the bones in adults which causes pain in the bones, and often joints and muscles) 
  • Osteoporosis (porous bones)
These issues in turn can lead to bone fractures, which can mean the end of independent living for the elderly.

Vitamin D deficiency is also blamed for many other health effects not related to our bones. People living further from the equator, where there are lower UV radiation levels, are at increased risk of:

  • Multiple sclerosis
  • Type 1 diabetes
  • High blood pressure
  • Tuberculosis
  • Schizophrenia 
  • Depression
All of these conditions have been linked with vitamin D levels in at least one study. 

Low levels of vitamin D have also been associated with increased risk of developing colorectal, breast, prostate and other cancers, as well as the metabolic syndrome.

Conversely, giving vitamin D supplements to people at risk of deficiency has been found to reduce the risk of multiple sclerosis and certain cancers, and prevent falls in the elderly.

But it’s important to note that many of these findings are based on preliminary research, and some authorities have questioned the benefits of vitamin D for reasons other than bone health and falls prevention. A review by the National Prescribing Service points out that many of the studies are observational, have design limitations or are contradictory.

A recent review of over 1000 studies by the US Institute of Medicine reported a general lack of evidence for a causal relationship between vitamin D deficiency and many of the associated disorders mentioned above – that is, it can’t be proven that vitamin D deficiency actually caused the problem. They were also critical of claims for benefits from taking unnecessary supplements, describing them as ‘overblown’, concluding there were no health guarantees other than for healthy bones (when taken with calcium).

Testing times

Vitamin D deficiency is largely symptomless, and may not be suspected unless the individual suffers an unusual fracture, or has one or more risk factors. Deficiency can be determined by measuring the levels of 25-OHD, the main form of circulating vitamin D. The degree of deficiency is determined according to the 25-OHD levels in the blood.
  • Vitamin D sufficiency >75 nmol/L
  • Sub-optimal Vitamin D 50-75 nmol/L
  • Mild deficiency 25-50 nmol/L
  • Moderate deficiency 15-25 nmol/L
  • Severe deficiency <15 nmol/L

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How much sun?


It’s recommended you get 5-15 minutes of sunlight to your unprotected face, hands and arms 4-6 times a week outside the hours of 10am-2pm (11am-3pm daylight savings time). 

However, this also depends on where you live, your skin colour, age and other factors. 

The map above provides recommendations based on location – people with dark skin may need 3-4 times as long.

Too much sunscreen?

One of the main reasons offered for widespread vitamin D deficiency is overzealous use of sunscreen and other sun protection – in other words, we’ve taken up advice to slip, slop and slap too well. 

Some have rejected this suggestion: one study from 1995 found that people using a placebo (non-protective) cream had similar levels of vitamin D to people using a SPF 17 sunscreen every day over summer – possibly because they didn’t use enough or reapply as often as necessary. 

But sunscreens these days tend to have a higher SPF (30+ is the norm) and besides this, people are likely spending more time indoors, particularly recreation time.

Good morning, sunshine!

When you go out for your daily dose of vitamin D, you might like to consider taking a morning, rather than afternoon, stroll. A study in mice has found that propensity to skin cancer fluctuates according to circadian rhythms. Mice are more likely to get skin cancer when exposed to UV radiation in the morning, thanks to low levels of an enzyme which repairs UV damage. 

Researchers have hypothesised that humans likely have higher levels of the enzyme in the morning (the opposite of mice, which are nocturnal) and may be less susceptible to cancer from UV damage in the morning than the afternoon. Further research is planned.

Pills and potions

If you’re at risk of vitamin D deficiency you could consider taking a supplement, with experts recommending a minimum of 400IU, and preferably 800IU per day. 

Vitamin D supplements are cheap, at around 10-16 cents per day, and usually come in a dose of 1000IU.

Many multi-vitamins contain vitamin D, but not in the amount required for preventing or treating deficiency. Also, vitamin D2 is considered less potent than vitamin D3. 

For people with a diagnosed deficiency greater amounts will be needed, possibly in conjunction with calcium – your doctor or other health professional will advise you.

A safe upper maximum for adolescents and adults is 4000IU per day. Long-term amounts over 10,000IU per day have been associated with kidney damage.

CHOICE verdict

It’s definitely a good idea to get enough vitamin D for bone health, whether through exposure to sun or supplements, and this may confer additional preventative health benefits. 

But too much sun poses its own risks, and taking vitamin D supplements other than to avoid deficiency is not going to make you healthier.

More information

The National Prescribing Service has an information sheet on vitamin D deficiency aimed at health professionals.

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