Review questions recent official vitamin D guidance

"Vitamin D pills branded 'waste of time' and could even be 'harmful' according to new research," The Sun reports. But, despite the headline, no new research has been done.

The news comes from a review of existing evidence published in the peer-reviewed British Medical Journal (BMJ), which questioned recent government advice on vitamin D supplements.

In July this year, Public Health England (PHE) recommended that everyone in the UK should consider taking 10mcg of vitamin D supplements daily in the autumn and winter.

They also recommended that people at risk of having low vitamin D levels should take supplements all year round.

The public health body was concerned that a combination of limited sunlight exposure – which stimulates the production of vitamin D – and a diet low in vitamin D may contribute to very low vitamin D levels, known as deficiency, in some people.

Vitamin D deficiency can lead to a range of complications, including a condition called osteomalacia, which makes bones soft, painful and more likely to break.

What is the basis for these current reports?

Researchers from the University of Auckland and the University of Aberdeen published a review in the BMJ that questions the evidence of PHE's recommendation about vitamin D supplements.

The researchers say that, despite much good-quality research into vitamin D, there is no evidence that taking vitamin D supplements alone reduces the risk of fractures or falls, or improves bone strength.

They say two studies into giving vitamin D supplements with calcium, which involved elderly women with very low vitamin D levels living in care homes, did show a reduction in fractures.

But studies in people who did not live in care homes did not find the same results.

The authors also looked at reports of other possible benefits of vitamin D, apart from bone and muscle health, and found "no consistent effect" of benefits.

As the authors of the review did not outline their search strategy for their evidence, it should be considered a narrative review (where researchers highlight evidence supporting their argument) rather than a systematic review (where researchers consider all available appropriate evidence).

A systematic review is considered to have more "weight of evidence".

The BMJ also included a "right of reply" piece by Dr Louis Levy, head of nutrition science at Public Health England.

Dr Levy makes the point that, "Vitamin D is found in only a small number of foods, including oily fish, red meat, liver and egg yolk, so it's not easy to get what you need from your diet alone."

"People with darker skin, from African, Afro-Caribbean, and south Asian backgrounds, may not get enough vitamin D from sunlight in the summer and should also consider taking a supplement all year round."

Most experts agree that people who are at high risk of low vitamin D levels may benefit from taking vitamin D supplements.

What is vitamin D deficiency?

Vitamin D is important for building healthy bones and muscles. Severe vitamin D deficiency can cause malformed bones (rickets) in children and osteomalacia in adults.

However, there's much scientific debate about what is considered a vitamin D deficiency and how much we need daily.

In July, PHE said everyone should aim to have a dietary intake of 10mcg of vitamin D daily, as it was difficult to say how much vitamin D is made by sunlight on skin.

Most of our vitamin D is made by sunshine on our skin. But in winter, sunlight in the UK is thought to be too weak to allow our skin to make vitamin D.

There's also vitamin D in some food – including oily fish like salmon, mackerel, herring and sardines, and red meat and eggs – as well as some breakfast cereals and fat spreads that have vitamin D added to them.

How does vitamin D affect you?

If you're not at high risk of a vitamin D deficiency, you probably get enough from a combination of food and sunshine during the summer months.

Find out how to get vitamin D from the sun without risking skin cancer.

PHE says adults should "consider" taking a daily supplement of 10mcg in the autumn and winter. The authors of the BMJ paper say this recommendation is unnecessary for most people.

But 10mcg is unlikely to be harmful, so it's a matter of individual choice. You should check that you're not taking vitamin D in multivitamin supplements as well.

Certain groups of people may be at higher risk of having a vitamin D deficiency:

• people who don't go outside very often – for example, those who live in care homes
• people who cover most of their skin when outside
• people with darker skin from African, Caribbean and south Asian backgrounds

PHE recommends these groups consider taking a supplement all year round. They also recommend daily supplements for pregnant women, babies and children aged four years old or younger.

Conclusion

So, who's right? The authors of the BMJ review are certainly correct in their argument that, ideally, we can get all the vitamin D we need through a combination of diet and sensible exposure to sunlight.

They are also right that the evidence does not show that people with normal levels of vitamin D benefit from taking supplements.

But we don't live in an ideal world. The truth is many people in the UK eat unhealthy, vitamin D-poor diets and also don't get enough exposure to sunlight.

A sensible approach would be to consider taking vitamin D supplements as recommended, but also be alert for possible signs of excessive vitamin D levels causing a build-up of calcium in the blood (hypercalcemia).

Warning signs and symptoms of hypercalcemia include loss of appetite, feeling and being sick, and needing to pee frequently.