Vitamin D deficiency in South Asians: why brown skin runs short in a sunny country

Two in three. That is the share of adults born in Southern and Central Asia, the Australian Bureau of Statistics grouping that includes India, Pakistan, Bangladesh, Nepal and Sri Lanka, whose blood tests showed vitamin D deficiency in the ABS’s 2011-12 Australian Health Survey: 67.4 per cent, against 17.0 per cent of Australian-born adults and 23.5 per cent of all adults. Researchers who pooled 65 studies covering 44,717 participants in India, Pakistan, Bangladesh, Nepal and Sri Lanka reported a similar figure: 68 per cent. The two figures come from different studies, years and groups of countries, so they are not a like-for-like comparison. Australian health bodies list dark skin, covering clothing and indoor work among the risk factors.

Why vitamin D deficiency hits South Asians harder

“Vitamin D forms in the skin when it is exposed to UV from sunlight,” Cancer Council Australia says, and naturally dark-skinned people “need more UV exposure to produce adequate levels of vitamin D as the pigment in their skin reduces UV penetration”. How much more is uncertain. A 2012 position statement in the Medical Journal of Australia, commissioned by the Australian and New Zealand Bone and Mineral Society and Osteoporosis Australia, says people with dark skin are likely to need sun exposures three to six times longer.

A newer sun exposure position statement, endorsed by organisations including Cancer Council Australia, Healthy Bones Australia and the Australasian College of Dermatologists, gives a lower range. Its full text, published by the Australian Skin and Skin Cancer Research Centre, says the extra time needed by people with Fitzpatrick skin types 5 and 6 “is unclear”, advises them to obtain two to four times more exposure than the times its tables give for lighter skin, and cites two studies that put the difference between type 6 skin and types 1 and 2 at between 1.3 and 8 times.

The 2012 statement’s table gives a person with moderately fair skin in Melbourne six to eight minutes of sun at 11am or 3pm daylight saving time in December and January, and 25 minutes at noon in July and August. Applied to the Melbourne winter figure, its three to six times multiplier for highly pigmented skin gives 75 minutes to two and a half hours.

Skin is only one factor. The 2012 statement lists dark-skinned people of either sex, particularly migrants and those who wear modest dress, among adult groups at high risk, alongside people working in enclosed environments such as offices, factories, warehouses, taxis and night shifts. Cancer Council Australia separately names “people who cover their skin for religious or cultural reasons”. Women fared worse than men in the South Asian review, published in BMC Public Health in October 2021: 76 per cent deficient against 51 per cent. Season matters too: in the ABS National Health Measures Survey 2022-24, 15.5 per cent of adults were deficient in summer and 26.1 per cent in winter, and in Victoria the winter figure was 32.2 per cent.

What the Melbourne clinic data showed

An audit of the records of 2,187 adults who attended a community health service in Kensington, Melbourne, between 2010 and 2012 found that, once people taking vitamin D supplements were excluded, migrants from countries in lower latitudes, between about 23 degrees north and south of the equator, were 1.48 times more likely to be vitamin D deficient than their Australian-born counterparts. The centre, the authors noted in BMC Cardiovascular Disorders in 2014, had given “higher priority to vitamin D testing in migrants”, so the comparison covers people the centre chose to test, not the whole community. A 2001 audit at the antenatal clinic of a Melbourne teaching hospital, published in the Medical Journal of Australia, found 66 of 82 veiled or dark-skinned pregnant women screened, 80 per cent, below the laboratory’s reference range.

What counts as deficient

The 2012 statement set adequacy at 50 nmol/L or more at the end of winter and graded deficiency as mild at 30 to 49, moderate at 12.5 to 29 and severe below 12.5. Healthy Bones Australia “recommends a vitamin D level of at least 50 nmol/L throughout the year”, and the South Asian review’s cut-off of 20 nanograms per millilitre is the same level in different units. In the ABS National Health Measures Survey 2022-24, one in five adults (20.6 per cent) was deficient, down from 23.8 per cent in 2011-12. That survey does not publish results by region of birth, but it found 29.2 per cent of adults born overseas deficient, against 16.1 per cent of those born in Australia.

What the Cancer Council and Healthdirect say about sun and darker skin

Cancer Council Australia’s advice: “When the UV Index is 3 or above (such as during summer), most people maintain adequate vitamin D levels just by spending a few minutes outdoors on most days of the week. In late autumn and winter in some southern parts of Australia, when the UV Index falls below 3, spend time outdoors in the middle of the day with some skin uncovered.” It says people in its at-risk groups “should consult their doctor for advice on whether they need to take a vitamin D supplement”, and adds: “Overexposure to UV is never recommended, even if you have a vitamin D deficiency.”

The revised position statement, published in the Australian and New Zealand Journal of Public Health in February 2024, sorts adults by skin cancer risk using the Fitzpatrick scale, which runs from type 1, pale skin that burns easily, to type 6. Its abstract says people with deeply pigmented skin “are at low risk of skin cancer but at high risk of vitamin D deficiency; routine sun protection is not recommended”. The Cancer Institute NSW summary says people with skin types 5 and 6, dark brown or black skin, “are advised where possible to spend sufficient time outdoors to achieve and maintain vitamin D status” and “do not need to apply sunscreen routinely, unless outdoors for extended periods”. For people at intermediate risk, the abstract says, “sun protection remains a priority, but individuals may obtain sufficient sun exposure to maintain adequate vitamin D status.”

Healthdirect, the national, government-owned health information service, says there are “usually no symptoms” of the deficiency, though mild bone pain, muscle weakness and tiredness are possible; long term, it can cause loss of bone density and a higher risk of osteoporosis in adults, and rickets in children. “Most people cannot get enough vitamin D from food alone,” it states.

Food and recommended intakes

Australia’s nutrient reference values agree that “Very few foods contain significant amounts of vitamin D”, name fortified margarine, fatty fish and eggs as the main Australian sources, and note evidence in Australia of high rates of deficiency among dark-skinned peoples, including “certain migrant groups and veiled women”. The adequate intake they set is 5 micrograms a day for adults aged 19 to 50, 10 micrograms for those aged 51 to 70 and 15 micrograms over 70, figures that “assume no, or minimal, exposure to sunlight”. These values date from 2006. The working group behind the sun exposure position statement considered them “likely too low in people with minimal sun exposure”.

The Medicare rule on vitamin D testing

MBS item 66833, in the schedule since 1 November 2014, covers a blood test for 25-hydroxyvitamin D only for a patient who meets one of 11 criteria. They include signs or symptoms of osteoporosis or osteomalacia, malabsorption, certain medicines and chronic renal failure, and, in criterion (e), a patient who “has deeply pigmented skin, or chronic and severe lack of sun exposure for cultural, medical, occupational or residential reasons”. The schedule fee is A$30.05, unchanged since the item began.

The Royal Australian College of General Practitioners says testing “is not routinely recommended for adults (including those who are pregnant), children or healthy infants”, but “may be appropriate for people at risk of vitamin D deficiency”. Its guidance for GPs advises against retesting within three months of a patient starting vitamin D replacement. Victoria’s Department of Health tells clinicians: “Routine screening for vitamin D is not recommended. Test adults and children with risk factors for low vitamin D.”

Where the official sources agree

In both ABS surveys, deficiency was more common among adults born overseas, and in 2011-12 it was most common among those born in Southern and Central Asia. Cancer Council Australia, Healthdirect, Healthy Bones Australia and Victoria’s Department of Health all list dark skin as a risk factor, and Medicare’s testing rules name deeply pigmented skin. On supplements, Healthdirect says: “Check with your doctor about the correct dose before taking any vitamin D supplements.”