People taking vitamin D supplements are probably wasting their time and money, says British genetics expert Prof Tim Spector.

Vitamin D is a “pseudo vitamin” that has created a “pseudo disease” of deficiency that vitamin companies, food manufacturers, public health departments, patient groups and charities encourage, he adds.

Spector is a rheumatologist, professor of genetic epidemiology and director of the TwinsUK Registry at Kings College in London. He was recently elected to the UK Fellowship of the Academy of Medical Sciences. He is the author of The Diet Myth, The Real Science Behind What We Eat.

One chapter deals with vitamin D misinformation. Spector has worked in vitamin D research for 20 years and prescribed supplementation to patients for 25 years. He changed his opinions and practice after robust research showing that supplementation for healthy people is risky.

Other experts insist vitamin D deficiency is commonplace, even in countries with abundant sunshine, such as SA. US endocrinologist Prof Michael Holick is professor of medicine, physiology and biophysics at Boston University Medical Centre and author of The Vitamin D Solution, A 3-Step Strategy to Cure Our Most Common Health Problems.

Holick has called vitamin D deficiency a “pandemic” and “the most common nutritional deficiency worldwide”.

But Spector does not buy it. He says that totality of the evidence shows that, except in rare cases, most people are not deficient in vitamin D.

One problem is that people are “still in love with vitamins a century after they were discovered. About half the population takes vitamins daily, despite zero benefits and increasing evidence of harm,” he says.

In many countries, vitamin D is the favourite supplement. Many “mistakenly believe it has the most proven benefits”, Spector says. Another problem is public health advice that is not evidence-based. Spector says: “Public health authorities are often out of date on the science.”

The largest study on vitamin D benefits, published in The BMJ in September, investigated more than 500,000 people and about 188,000 fractures from 23 cohorts in different countries. Researchers from Holland, Canada, the US, UK, China and Sweden found no association between vitamin D levels and fracture risk over a lifetime.

The study is observational and cannot show causation. However, genes influence vitamin D levels strongly, Spector says. Therefore, the researchers used genetic markers for vitamin D blood levels, called Mendelian randomisation (MR), to avoid “normal biases of observational studies” – that include confusing cause and disease consequence.

Critics attacked the study as serving “Big Pharma” interests. Spector dismisses that. A pharmaceutical company makes the UK’s biggest-selling vitamin, a vitamin D and calcium combination, he says.

“It’s not a little cottage industry. The idea that vitamins are a nice, quaint, community, eco-friendly business and Big Pharma is evil is silly,” he says. It is worth noting, Spector adds, that more than 95% of world’s vitamins and supplements are made in factories in China.

Governments in the US and UK still believe the evidence for vitamin D’s health benefits is overwhelming and every adult should take a supplement for at least six months, preferably a year-long, says Spector.

SA’s department of health recommends regular intake of calcium and vitamin D to keep bones strong. Spector says these are “knee-jerk reactions” by governments wanting to be seen to be doing something for population health – and because vitamin D is cheap.

Much of the strong belief in vitamin D benefits came from studies in care-homes in the 1980s, says Spector. “These were probably flawed and never replicated.”

Most positive published studies in 137 diseases turned out to be spurious, he says. Experts widely believed that vitamin D supplements prevented cardiovascular disease. Meta-analyses and large-scale genetic MR studies ruled this out.

An aggravating factor is the lack of international consensus on what vitamin D deficiency is. Doctors consider a “normal” level from 50 to 80 nanomole (nmol) per litre of blood, Spector says. Recent research suggests that 30nmol is sufficient. Clinical deficiency is often “clear-cut at less than 10nmol”.

“Wrongly labelling millions of people as vitamin D-deficient causes stress and over-medicalisation,” he says.

Despite its star status as the “sunshine vitamin”, vitamin D would not be called a vitamin today. Spector says: “Doses needed are too large, the body can synthesise it from skin and it is a steroid precursor.”

Most people wrongly assume that a vitamin is safe and the more you take, the better. Vitamin D is not safe, he says. It is fat-soluble, meaning that high levels build up in the body.

Official recommendations are usually modest doses – 10 micrograms or 400 IU. However, “some will inevitably overdo these and take in other sources in cod liver oil tablets or fortified milk, orange juice or bread”, Spector says.

People are also buying high-dose vitamin D supplements of 4,000-20,000 IU on the internet. Patients with high vitamin D blood levels (over 100nmol) are becoming routine in Spector’s clinic and elsewhere. Researchers are increasingly reporting toxic overdoses, he says. This can cause a build-up of calcium in the blood (hypercalcemia) and kidney problems.

Spector says there is a rare medical role for vitamin-D treatment in severe deficiency or those who are bed-bound. South African and other research adds people infected with HIV and TB and Indian and Asian women who walk around fully clothed to that list.

The rest of us should avoid treatment with an “imposter vitamin” for a “pseudo-disease”, Spector says.

Healthy people should have a healthy lifestyle, get vitamin D from small doses of sunshine daily and a “rich diversity of real food”. Good sources are fish, oil, mushrooms and dairy products.

“We should trust that thousands of years of evolution would cope with a natural drop in vitamin D levels in winter without us snapping our limbs,” Spector says. “We must also seriously question the worldwide trend of adding unregulated vitamins to processed food.”