Vitamin D has been a source of interest for years because of its benefits to our body’s immune system and its importance to our bone health.

But since the covid-19 pandemic it has also become an element of controversy given the spread of internet content mentioning it as a key factor in our body’s fight against the disease.

Although it must be said that the role of vitamin D in the fight against the coronavirus is still being investigated by scientists and there is no consensus, it is notable that the considerable increase in the number of people lacking adequate levels of this vitamin in recent years comes just after the period when we were forced to confine ourselves to our homes because of the pandemic.

Hence, since then, sales of supplements of the so-called “sunshine vitamin” have skyrocketed in many parts of the world.

However, many experts warn that excessive intake can be counterproductive.

In the face of so much information and misinformation we decided to find out with the help of specialists and scientific articles who are the people who should take the supplements, what diseases it can prevent and what would be an ideal level in the blood.

Let’s start with what is already known about vitamin D.

Basic concepts

The first thing to point out is that, despite its name, vitamin D is not a vitamin but a hormone.

When it was discovered more than a century ago by a team led by the American biochemist Elmer McCollum, it was thought to be a vitamin and identified by the letter D.

Decades later, with further research and the detail of its molecular structure, it was determined that it was a hormone.

Among its properties, it has been shown that it regulates the amount of calcium and phosphorus in the body, and these are essential for the growth and maintenance of bones, teeth and muscles. In other words, vitamin D is very important for bone and muscle health.

We also know that it can be obtained in three ways: through our body’s own production thanks to sun exposure, through food (especially oily or fatty fish) and through supplements.

With any of these three sources it is possible to reach the adequate level of vitamin D needed by the body, although many variables must be taken into account to know if we are doing it correctly.

A person with fair skin does not react the same way as a person with darker skin and the impact of the sun’s rays is not the same in Ecuador as in temperate zones.

There is also “a lack of nutritional education to understand that food will hardly be enough to supply the need,” nutritionist Marcela Mendes explained to BBC News Brazil.

“The main foods with vitamin D are wild salmon, mushrooms and oily fish. What is the real application of this in our population? The intake (of these foods) would have to be daily for us to really have a source,” said Mendes, PhD in Nutritional Sciences from the University of Surrey (England) and member of the Universities Global Partnership Network (UGPN) vitamin D research group.


Worldwide data collected in an article in the journal Nature show that the percentage of vitamin D deficiency in the population in the United States reaches 24%, while in Canada it is as high as 37% and in Europe 40%.

It is believed that the percentage in Latin America is considerably lower given the constant exposure to the sun most of the year in the region, but this does not mean that it is completely free of the problem.

In one of the few studies conducted on the subject in November 2022 in Brazil for the Journal of the Endocrine Society of the University of Oxford, endocrinologist Marise Lazaretti-Castro found vitamin D deficiency in 12.1% of people in Salvador, 20.5% in São Paulo and 12.7% in Curitiba.

One of the causes, they mention, is due to the current lifestyle that causes a decrease in sun exposure, as we stay at home more and use sun protection.

To counteract this tendency, the consumption of supplements is recommended, but not in all cases and always in moderation.

The first thing that is necessary is to check the levels of the hormone circulating in the body and then a doctor or nutritionist can decide whether supplements are necessary or not.

Although it may vary depending on the characteristics of each person, the level of vitamin D that a person should have ranges between 50 and 250 nanomoles per liter.

To maintain this level, adolescents and adults need about 15 micrograms per day or 600 IU (international unit established by the Biological Standardization Committee of the World Health Organization).

Nutritionist Marcela Mendes says to perceive, by the population and some health professionals, the use of vitamin D as something “miraculous”.

“It is important to point out that supplements are a very important strategy: there are many situations in which a supplement is needed and it is the supplement that is going to solve the problem,” Mendes commented.

“But today, we see people taking 5,000, 10,000 IU a day hoping that the molecule will perform some specific action,” he added.

For Dr. Marise Lazaretti-Castro, an overdose carries risks.

“In the long term, it will lead to vitamin D intoxication, which is serious. Calcium rises a lot in the blood and that gives many adverse effects, such as nausea, vomiting, diarrhea. It can also cause loss of appetite, weight loss, polyuria, dehydration, renal failure, loss of renal function…. Death can even occur.”

“Vitamin D deficiency is bad, but so is excess,” he warns.

The role of vitamin D in disease prevention and treatment.

Although the benefits of vitamin D for bone health are already known, the hormone’s so-called “extraskeletal effects” are being studied, and in full swing.

In the first quarter of this year alone, scientific papers have been published investigating the role of vitamin D in multiple sclerosis, dementia, asthma, melanoma skin cancer and many other diseases.

The hypothesis that the hormone may have a role in the prevention or treatment of diseases is due, in part, to the fact that vitamin D receptor genes have been found in various types of cells in the human body, from neurons to lymphocytes. That is, if there are receptors, it is likely that vitamin D has some function in that cell.

In addition, guinea pig studies in which these receptors were excluded showed that mammary glands became more prone to breast cancer; heart muscle, to hypertrophy; prostate, to hyperplasia; and liver, to fattening.

However, there are questions about whether the link between vitamin D and health effects is one of causation, correlation or even “reverse causation,” according to endocrinologist Marise Lazaretti-Castro.

“Since vitamin D depends on sun exposure, if you are sick, you will not be exposed to the sun as much. It’s what we call reverse causality: the disease is producing the lower amount of vitamin D, not the other way around,” she says.

In order to prove causality between vitamin D and some effect on health, the best way would be with studies through randomized controlled clinical trials, which consist of tests with volunteers.

But even the largest such study, the VITAL study in the United States, ran into obstacles.

It investigated the relationship between vitamin D, cancer and cardiovascular disease by following 25,817 volunteers for an average of five years.

They were divided into a group that received supplements with a high dose of vitamin D (2,000 IU) and another that received a placebo.

The study concluded that vitamin D did not produce a significant reduction in the risk of cancer or cardiovascular disease. Nor were deaths from cardiovascular disease reduced, but in the case of cancer, the reduction in mortality was 17%.

But Lazaretti-Castro explains that the VITAL study faced a hurdle often encountered in clinical trials with vitamin D: it is unethical to leave the placebo group of volunteers deficient in the hormone.

So the U.S. experiment allowed all the volunteers, whether they were in the control group or not, to take 800 IU per day of supplements, which is a good amount.

The difference in the group that received the high doses is that these people received even more vitamin D.

The endocrinologist has also participated in four editions of a conference dedicated to the controversies surrounding the hormone where debates range from the ideal reference values for vitamin D in the blood to from what amount a high dose of vitamin D presents health risks.

“There is consensus on two points: 25-hydroxyvitamin D levels below 12 ng/mL are clearly deficient at all ages and levels above 30 ng/mL are clearly sufficient. In contrast, there is disagreement on how to classify levels between 12 and 30 ng/mL,” notes a text with the conclusions of the III International Conference on Vitamin D Controversies, held in 2019.

For Marcela Mendes the main certainty that remains is that “we know that the future path of vitamin D is to discover much of its importance”.

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All content in this column is for general information only, and should not be understood as a substitute for medical advice from your doctor or any other health care professional. GLM is not responsible for any diagnosis made by a user based on the content of this site. The GLM is not responsible for the content of external Internet sites cited, nor does it endorse any commercial products or services mentioned or advice given on any of the sites. Always consult your GP if you are concerned about your health.

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