Vitamin D supplements: the case for and against


What do you know about the benefits and risks of vitamin D supplementation?

Supplements and complementary medicines are a continuously contentious topic among Australian doctors, pharmacists, manufacturers and consumers.

This month a review published in the BMJ concluded that current evidence does not support the use of vitamin D supplements to prevent disease, except potentially in those at high risk.

Associate Professor Mark Bolland and colleagues at the University of Auckland, New Zealand, and the University of Aberdeen, Scotland concluded that those at high risk of vitamin D deficiency should be advised about sunlight exposure and diet, and consider low-dose supplements on an individual basis.

Everyone else is recommended to get regular short bursts of sunshine and eat a healthy balanced diet.

Mixed messages

Vitamin D supplementation across the board is often recommended and consumers can get mixed messages from organisations, healthcare practitioners and the media.

In July, a committee of independent experts recommended that everyone in the UK should take vitamin D supplements. Complementary Medicines Australia applauded the move, highlighting the importance of sunlight but also encouraging supplementation in the Australian population.

Carl Gibson, chief executive officer of CMA, said at the time: “Whilst this latest report was UK based, it is a timely reminder that with between 31% and 58% of Australians found to suffer from vitamin D deficiency, we cannot assume that Australians receive adequate vitamin D from casual exposure to sunlight.

“A responsible and preventative approach is to acknowledge that a large proportion of the population is vitamin D deficient and not just those at high risk.

“This is where vitamin D-fortified foods and vitamin D supplements come into the disease prevention equation. More of us should be supplementing vitamin D as it is a cost-effective and easy approach to avoiding vitamin D deficiencies,” Gibson says.

Gibson also cited a doctor quoted in MJA InSight who suggested that many GPs overtest for vitamin D deficiency.

“The [obvious question is], if you know your patient is at risk — sits in an office all day, or has other risk factors — why test them? Why not just supplement them?” said Professor Robyn Lucas, an epidemiologist with the Australian National University’s College of Medicine, Biology and Environment.

Maintaining sufficient Vitamin D levels

A working group commissioned by the Australian and New Zealand Bone and Mineral Society (ANZBMS) and Osteoporosis Australia (OA) has developed a position statement that outlines the latest research about vitamin D and adult health.

Published in the Medical Journal of Australia, the position statement explains that for most Australians, the main source of sufficient vitamin D is skin exposure to sunlight.

“There are experimental data indicating that exposure of around 15% of the body surface (arms and hands or equivalent) … near the middle of the day will result in the production of about 1000 IU (25 µg) of vitamin D,” write the researchers.

“Achieving this exposure on most days should generally, though not always, be sufficient to maintain vitamin D levels in the body.

“Most adults are unlikely to obtain more than 5%–10% of their vitamin D requirement from dietary sources. The main source of vitamin D for people residing in Australia and New Zealand is exposure to sunlight,” they say.

At-risk groups for vitamin D deficiency

There are specific reasons that people don’t achieve sufficient levels of vitamin D, says the working group.

  1. Elderly or disabled people in residential care: Lack of any skin exposure to sunlight, through confinement indoors, is a common issue.
  2. Dark-skinned people, particularly if modest dress is worn: Vitamin D synthesis is reduced by clothing, and people who wear covering clothing for cultural or religious reasons are an at-risk group.
  3. Fair-skinned people and those at risk of skin cancer: Sun avoidance behaviour of fair-skinned people increases their risk of vitamin D deficiency.
  4. Obese people: Vitamin D enters fatty tissue and may not be readily released – so obesity results in lower vitamin D levels after receipt of oral or cutaneously synthesised vitamin D.
  5. People working in an enclosed environment, such as office workers, factor or warehouse workers, taxi drivers, and night-shift workers: Lack of any skin exposure to sunlight, through confinement indoors, is a common issue.

Providing advice to patients

The working group suggests that for people with moderately fair skin, adequate vitamin D levels are likely to be maintained in summer by a walk outside with arms exposed for 6-7 minutes mid-morning or mid-afternoon. In winter, walking outside at midday for 7-40 minutes, with as much bare skin exposed as feasible, is likely to be helpful.

People with darker skin usually need sun exposure 3-6 times longer than for those with fairer skin.

Recommending increased sun exposure at the levels above should be the first line of treatment.

However, while the ANZBMS and OA working group suggests Vitamin D supplementation without initial testing can potentially be recommended for those at obvious high risk – such as those with very dark skin or in residential care – it suggests the majority of people should be first screened for vitamin D levels before supplementation is begun.

“I wouldn’t start treating vitamin D deficiency unless I had some clinical evidence – confirmation with a blood test,” says Sydney pharmacist Nick Logan, who owns and manages Nick Logan Pharmacist Advice.

“I would recommend people to see their doctor if they’re over 50, have dark skin, wear a lot of clothes or are confined indoors.

“If it’s for osteoporosis, then weight-bearing exercise during daylight hours is beneficial.”

Logan adds that it is important to look at the evidence when it comes to supplements.

“I think going forward in Australia, particularly with the conversations happening about complementary medicines, the ones that have an evidence base should be the ones we focus on and talk to patients about,” he says.

Exercising caution with supplements

Pharmacists should exercise caution when recommending vitamin D supplements. The main concerns with excessive vitamin D levels are hypercalciuria and hypercalcaemia.

As Nowson et al. explain, vitamin D toxicity can be caused by excess oral intake through supplementation, but not by prolonged exposure of the skin to sunlight.

Cod liver oil – sometimes used for vitamin D supplementation – also contains vitamin A, which can be toxic at high doses.

Other experts warn that people who choose to take vitamin D supplements should avoid taking multiple supplements containing the vitamin, as the doses will add up.

“Excess intake of vitamin D can result in hypercalcaemia, demineralisation of bone, soft tissue calcification, and renal damage,” explains Louis Levy, head of nutrition science at King’s College London.

Several randomised trials have also reported that patients taking large doses of vitamin D had an unexpected increased risk of falls and fractures, suggesting the vitamin can have unexpected toxic effects, says Tim Spector, professor of genetic epidemiology at King’s College London.

“Patients with very high vitamin D levels (100-180 nmol/L) are becoming routine in clinical practice,” says Professor Spector.

References:

Complementary Medicines Australia 2016, Media release: CMA welcomes vitamin D guidance

Bolland, M, Avenell, A & Grey A 2016, ‘Should adults take vitamin D supplements to prevent disease?’, The British Medical Journal.

Nowson et al. 2012, ‘Vitamin D and health in adults in Australia and New Zealand: a position statement’, Medical Journal of Australia.

Spector, T & Levy, L, ‘Should healthy people take a vitamin D supplement in winter months?’. The British Medical Journal.

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