Vitamin D: sunshine vitamin or snake oil for pseudo-disease?


By Marika Sboros

Vitamin D is widely known as the “Sunshine Vitamin”. It’s one reason for the love affair with vitamins, a century after scientists discovered them. It’s also the reason that nutrition science is looking decidedly dodgy these days.

That affair has spawned the billion-dollar global supplement industry. It has also created “pseudo-diseases” in its wake, says British geneticist Prof Tim Spector. One of those pseudo-diseases is Vitamin D deficiency.

Spector is professor of genetic epidemiology and director of the TwinsUK Registry, at Kings College London. Spector has looked at another confounding variable in nutrition research these days: We have ignored a new “virtual” organ in our bodies for the digestive and endocrine system, he says. It is the microbiome that he calls our “second brain”.

The microbiome is the term for the community of microbes, around 100 trillion of them, that live inside our guts, mainly in the lower intestine. Research also shows that a healthy microbiome is essential for health in body and mind.

Prof Tim Spector

One problem, as Spector identifies, is that too many people believe in a “miracle vitamin pill”. It makes them feel that “they are doing something”. Given the research results, many experts look on supplements as close to “snake oils”.

Spector doesn’t go quite that far. However, he has said that about half the population takes vitamins daily, despite zero benefits, with increasing evidence of harm.

He is author of a seminal work on gut health and food: The Diet Myth: The Real Science Behind What We Eat.

Spector spoke on the topic at the recent Swiss Re conference in Zürich, Switzerland, in June 2018. The conference was a joint initiative between the global reinsurer and The BMJ. He gave a presentation at the session on Food For Thought, The science and politics of nutrition.

Food better than pills in gut health

His research suggests that fermented foods may be a better option than popping pills to feed the microbiome. These foods include yoghurt, sauerkraut, kimchi (a Koren fermented vegetable) and kefir (fermented milk drink native to Eastern Europe).

Fermented foods are more helpful, says Spector, because they contain fibre along with cultures. They are also more likely to get into the lower gut than taking a pill.

In the article below, Spector looks at why vitamin D is a “pseudo-vitamin”. (Editor’s note: After responses to this article, it is clear that vitamin D is  problematic because of controversy around just what it is. Some experts say it is a “steroid hormone”. Others have another view: they say it is a “vitamin in the truest sense of the word”. )

Here’s why Spector argues that it is more likely a pseudo-vitamin that has led to a “pseudo-disease”.

By Tim Spector, King’s College London

We are still in love with vitamins a century after they were discovered, with half the US and UK population taking a supplement. vitamin D – the sunshine vitamin – is the favourite. Many believe it  to have the most proven benefits.

Governments, including the UK government, have said that the evidence for vitamin D’s health benefits is so overwhelming that every adult should take it as a supplement for at least six months of the year.

From rickets to cancer

Vitamin D was first used to cure rickets in Victorian children living in urban poverty. Doctors now give it routinely to prevent and treat brittle bone disease (osteoporosis) and fractures. It has been associated with a reduced risk of over a hundred common diseases in observational studies, ranging from depression to cancer.

The BMJ has reported the largest ever clinical study on the benefits of vitamin D in preventing fractures, with over 500,000 people and around 188,000 fractures from 23 cohorts from many countries. As genes strongly influence vitamin D levels, the researchers used genetic markers for vitamin D blood levels (called Mendelian randomisation or MR). This is to avoid the normal biases of observational studies, such as confusing cause and consequence of disease and the effects of other related health behaviours (so-called “confounders”).

Mendelian randomisation explained.

The results showed no association between vitamin D levels over a lifetime and the risk of fracture. This latest study contradicts the UK government’s recent view but not a host of earlier clinical trials.

No effect on fractures

In 2014, a review and meta-analysis of 31 vitamin D supplement trials found no effect on all fractures. Much of our strong belief in the benefits of vitamin D came from studies of supplements in care homes in the 1980s. These were never replicated and were probably flawed.

In a more recent meta-analysis of 33 randomised trials of over 50,000 older adults, supplementation with calcium or vitamin D had no effect on the incidence of fractures. There were also no clear benefits on muscle strength or mobility.

So, if all the data points to vitamin D failing to prevent fractures, why worry about all the people with low blood levels of the vitamin? Vitamin D deficiency has become a modern epidemic with a fifth of the UK and US populations reported to have low levels. Will they be more susceptible to other diseases and cancer?

No consensus on deficiency

There is little agreement on what vitamin D deficiency is. Deficiency levels are arbitrary with no international consensus and confusion caused by different units in the US. A “normal” level can vary from 50 to 80 nanomole per litre of blood. But recent studies suggest 30nmol is quite enough.

While clinical deficiency (<10nmol) is often clear-cut, wrongly labelling millions of people as vitamin D deficient causes stress and over-medicalisation. Most people assume calcium and vitamin D are safe and the more you take the better.

My clinical practice changed when studies showed calcium supplements, as well as being ineffective against fractures, may cause heart disease. Prescriptions are now dropping.

Vitamin D is fat-soluble, so high levels can build up in the body. While recommendations for supplements are usually with modest doses (10 micrograms or 400 international units (IU)), some people will inevitably overdo these, taking other sources in cod liver oil tablets or in fortified milk, orange juice or bread.

Vitamin D ‘far from safe’

More worrying, people increasingly buy high-dose supplements of 4,000-20,000IU on the internet.

Patients with very high vitamin D blood levels (over 100nmol) are becoming routine in my clinic and elsewhere. And researchers are increasingly reporting toxic overdoses. Several randomised trials have shown that patients with high blood levels or taking large doses of vitamin D (above 800IU) had an unexpected increased risk of falls and fractures.

Vitamin D is far from safe.

It can no longer be recommended for use in other conditions; the vast majority of the positive published studies in 137 diseases were reviewed as spurious. Many have widely believed that vitamin D supplements prevented cardiovascular disease. But meta-analyses and large-scale genetic MR studies have ruled this out.

You can get enough vitamin D from food and a bit of sunlight.


We have created another pseudo-disease that vitamin companies, patient groups, food manufacturers public health departments and charities encourage. Everyone likes to believe in a miracle vitamin pill and feels “they are doing something”.

Vitamin D, despite its star status, would not be called a vitamin today. The doses needed are too large, the body can synthesise it from skin and it is a steroid precursor. Instead of relying on this impostor, healthy people should get vitamin D from small doses of sunshine every day. They should also get it from food, such as fish, oil, mushrooms and dairy products.

We should also trust that thousands of years of evolution would cope with a natural drop in vitamin D levels in winter without us snapping our limbs. About half the population take vitamins daily, despite zero benefits, with increasing evidence of harm.

We must now seriously question the worldwide trend of adding unregulated vitamins to processed food.

While vitamin D treatment still has a rare medical role in severe deficiency, or those bed bound, the rest of us should avoid being “treated” with this steroid for this pseudo-disease. We should focus on having a healthy lifestyle, sunshine. And importantly, we should save our money and energy on eating a rich diversity of real food.The Conversation



  1. I suspect the problem with studies on vitamins and other supplements is that while they are beneficial for people with a deficit they don’t do anything for people who are already replete. I remember diabetics on a forum trialling chromium and finding only some of them benefited. Getting micronutrients especially fat-soluble ones from food is better than taking a pill because you get all the other micronutrients. Getting vitamin D from sun exposure is good because you also get NO. Probably avoiding sun exposure and fat is the reason for the deficiency in the first place. Maybe they shouldn’t have told us to do that.

  2. Very confusing. I watched “D is for Debacle” by Ivor Cummins on YouTube. His presentation about the importance of Vitamin D3 is the polar opposite to this advice.

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