About four million Australians now suffer from a vitamin D deficiency, according to the latest ABS data. One of the main reasons offered for this widespread vitamin D deficiency is overzealous use of sunscreen and other sun protection – in other words, we’ve taken to slipping, slopping and slapping a little too well.
While some have rejected this suggestion, it could be explained by a few factors – for example, sunscreens now having higher SPF ratings (30+ is the norm), and people being more likely to spend more time indoors, particularly recreation time.
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; 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).
Apart from supplements, vitamin D occurs in two forms – D3 and D2. Our main source of vitamin D comes from exposure to sunlight, when a steroid in the skin (called 7-dehydrocholesterol (7-DHC)) is converted to vitamin D3 (cholecalciferol) through the action of solar UVB radiation.
Smaller amounts of vitamin D3 can also be obtained from certain foods such as fatty fish, eggs, meat and fortified foods such as margarine and certain low-fat milks.
Vitamin D2 (ergocalciferol) comes from fungi, and may be used in supplements. However, most adults are unlikely to get more than 5-10% of their vitamin D needs from dietary sources. Also, Vitamin D2 is considered less potent than vitamin D3.
In addition to getting enough sun, it's important to eat the recommended dose of calcium as well as undertaking weight-bearing or muscle-strengthening exercises for optimal bone and muscle function.
If you think you're at risk of vitamin D deficiency you could consider taking a supplement.
If the ideal amount of sun exposure can't be reached, vitamin D from dietary sources and supplements is recommended in order to prevent deficiency.
- At least 600 IU (15 µg) per day is recommended for people aged under 70.
- 800 IU (20 µg) per day is recommended for those aged over 70 years.
People in high-risk groups may require higher doses. This also depends on where you live, your skin colour, age and other factors.
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.
Vitamin D supplements are cheap, 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.
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.
Recommended sun exposure times
For most people, sensible sun exposure is the easiest way to increase your vitamin D levels. But how much sun do you need? In order to maintain adequate vitamin D levels it's recommended that people with moderately fair skin get 6-7 minutes of sun with arms and hands exposed outside the hours of 10am-2pm (11am-3pm daylight savings time). In winter, this translates to7-40 minutes (depending on your location) at noon, with as much bare skin exposed as possible. People with dark skin may need 3-6 times as long.
|Recommended sun exposure times
(minutes, in order of shortest to longest times in winter)
Jul–Aug, at 10 am or 2 pm
Jul–Aug, at noon
Dec–Jan, at 11 am or 3 pm
When you go out for your daily dose of vitamin D, you might like to consider taking a morning stroll, rather than afternoon. A study in mice has found that propensity for 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. But further research needs to be done before any recommendations for humans can be made.
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, which 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 off doing what it should do, elsewhere in the body.
- Elderly people have lower concentrations of 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.
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(OH)D (the main form of circulating vitamin D), however, testing is only recommended for those with a moderate to high risk of deficiency.
The degree of vitamin D deficiency is determined according to the 25(OH)D levels in the blood. Levels of 25(OH)D in the blood above 50 nmol/L are considered adequate vitamin D levels. Anything less than 12.5 nmol/L is considered to be a severe vitamin D deficiency.
While symptoms are more or less non-existent, the result of a vitamin D deficiency can be more serious. 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), and
- Osteoporosis (porous bones).
These issues can lead to bone fractures, which can mean the end of independent living for an elderly person.
Vitamin D deficiency is also blamed for many other health effects not related to our bones. But whether or not vitamin D is actually the cause of these conditions is still unclear.
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,
- Schizophrenia, and
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. In addition, 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 fall prevention. A review by the National Prescribing Service points out that many of the studies are observational, have design limitations, or are contradictory.
A review of over 1000 studies by the National Academy 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 beneficial claims linked to taking supplements, saying there were no health guarantees other than for healthy bones (when taken with calcium).
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. Talk to your doctor first if you're worried you might be deficient in vitamin D for any reason.
Stock images: Getty, unless otherwise stated.