The number of vitamin D supplement prescriptions written for children in primary care in the UK has surged 25-fold in under 10 years reveals GP prescribing data.

In an analysis published today in BMJ Open, researchers found that increasingly higher doses and an absence of a prior diagnostic blood test featured in more than half of the annual prescriptions written.

Vitamin D, which is usually sourced from sunlight and diet, is essential for healthy teeth, bones, and muscles. A severe vitamin D deficiency can cause rickets and seizures in children and several studies have linked low levels of the vitamin with various conditions, including diabetes, asthma, and eczema. However, most clinical trials have failed to show any meaningful impact of supplementation on improving health and it is not clear what impact vitamin D insufficiency has.

Researchers including Dr Mandy Wan, Institute of Pharmaceutical Science, drew on information from medical records submitted by GPs to the Health Improvement Network (THIN) between 2008 and 2016 inclusive. The THIN database contains anonymised data from 744 general practices and around 16 million patients, equivalent to more than 6% of the UK population.

The results showed that:

• During the study period, 12, 277 children from 723 general practices were prescribed vitamin D supplements for the first time.
• Girls were more likely than boys to be prescribed these supplements, and prescribing rates were higher in England than elsewhere in the UK.
• Older age, social deprivation, and black, Afro-Caribbean and Asian ethnicities were all associated with higher rates of vitamin D prescribing.
• By 2016, the prescribing rate was more than 25 times higher than it had been in 2008, rising from 10.8 to 276.8/100,000 person-years*. This trend was particularly noticeable among 12-17-year olds, among whom girls were nearly twice as likely to be prescribed a vitamin D supplement as boys. But increased prescribing rates also occurred across all the other age groups: 0-6 months; 6 months-4 years; 4-11 years.
• Overall, between 29% and 56% of prescriptions annually had no linked blood test results for vitamin D levels recorded in the 3 months before the prescription was issued.
• Less than a third (29.5%) of all children prescribed the supplement had symptoms indicative of vitamin D deficiency, including aches and pains, tiredness or fatigue. Among those with no vitamin D levels recorded beforehand, symptoms were recorded for just one in six.
• Prescribed doses varied greatly, with a tendency to increasingly prescribe therapeutic (pharmacological) doses to children, irrespective of their vitamin D levels.

Official guidance recommends prescribing therapeutic doses of supplementary vitamin D only to those diagnosed with vitamin D deficiency.

*Person years are calculated as follows: If 10 patients participated in a study on heart attacks for 20 years, and 2 patients had heart attacks by year 5 and 15, respectively, that would add up to 180 person years [(8 x 20) + (1 x 5) + (1 x 15)]. The rate of heart attack is said to equal to 2 per 180 person years (or 1.1 per 100 person years)