Vitamin D supplements don’t work if you’re too fat, study warns

Vitamin D supplements may not work if you’re overweight, a study suggests.

Supplementing the sunshine vitamin is vital for keeping bones strong and strengthening the immune system, and may lower the risk of death from cancer.

But a review of existing evidence found the benefit only applies to people who are a healthy weight.

People who are overweight or obese — a risk factor for a host of health issues including cancer, heart disease and stroke — had ‘minimal’ benefit from the pills.

Vitamin D supplements can help ward off cancer and autoimmune diseases, but only if you are a healthy weight, a study suggests (file photo)

Scientists believe people who have too much fat in their bodies struggle to metabolize vitamin D supplements for use in the body.

The study found they had significantly lower levels of vitamin D in their blood compared to healthy people taking the same pills.

Dr Deirdre Tobias, an epidemiologist at the Brigham and Women’s Hospital who led the research, said: ‘We observed striking differences after two years, indicating a blunted response to vitamin D supplementation with higher body mass index (BMI).

‘There seems to be something different happening with vitamin D metabolism at higher body weights, and this study may help explain diminished outcomes of supplementation for individuals with an elevated BMI.’ 

For the study — published today in JAMA Network Open — researchers re-analyzed data from one of the largest and longest-running vitamin D trials to date, the US-based VITAL study.

This tracked 26,000 people who took daily vitamin D supplements for about five years between 2010 and 2018.

All the participants were over 50 years old, and did not have cancer or a cardiovascular disease at the start of the study. 

Half took pills containing 2,000 international units (IU) of vitamin D per day, or five times the recommended daily intake of 400IUs daily from US health authorities.

The other half were placed in the placebo group who took a dummy pill.

Results showed there was an overall 20 percent lower risk of death from cancer, although this was not significant.

Researchers from Brigham wanted to see whether bodyweight had played a role in this reduction.

They then re-analyzed data from a smaller subset of 16,000 participants who also had blood work done when the trial began and up to two years into the study.

The sample included 6,600 people who had a body mass index (BMI) in the overweight category and 4,400 who were in the obese or morbidly obese group. 

Results showed that both groups saw a rise in vitamin D levels in their blood during the study.

But the uptick was significantly higher in the group that was not overweight or obese.

Dr Tobias added: ‘This study sheds light on why we’re seeing 30 to 40 percent reductions in cancer deaths, autoimmune diseases and other outcomes with vitamin D supplementation among those with lower BMIs.

‘But minimal benefit in those with higher BMIs, suggesting it may be possible to achieve benefits across the population with more personalized dosing of vitamin D.

She added: ‘The analysis of the original VITAL data found that vitamin D supplementation correlated with positive effects on several health outcomes, but only among people with a BMI under 25. 

Scientists suggested overweight or obese people may have lower levels of vitamin D because fat cells are better at absoring the vitamin than others, and could be extracting more of it from the blood.

They also suggested that being overweight could ‘impair’ the body’s ability to make or process vitamin D, leading to lower levels.

Estimates from the Centers for Disease Control and Prevention (CDC) suggest approximately 42 percent of the US population has a vitamin deficiency. 

The VITAL trial was a randomized, double-blind, placebo-controlled trial carried out in the US. It was funded by the National Institutes of Health.

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What is vitamin D and how do I get it? 

Vitamin D is a type of vitamin that the human body gets from both diet and produces when exposed to sunlight. 

What does it do?

It helps regulate the amount of calcium and phosphate in the body.

These nutrients are needed to keep bones, teeth and muscles healthy.  

People who don’t get enough vitamin D can suffer from bone deformities such as rickets in children and osteomalacia (a softening of the bones) in adults.   

How do I get enough vitamin D?

In the U.S. most people will get the vitamin D they need from sunlight between April and September as long as they go outside.

The body naturally produces vitamin D when exposed to sunlight.

Vitamin D is also found in foods such as oily fish, liver and egg yolks.

Do I need to take a supplement?

Medics say people should consider taking a vitamin D supplement in the winter month when sunlight is weaker.

Other people may need to take vitamin D throughout the year due to being housebound, or if they have dark skin which reduces the amount of sunlight their skin absorbs. 

Children aged one-to-four years old should also be given a daily vitamin D supplement of 10micrograms(μg) of throughout the year.

What happens if I take too much? 

Taking too much over a long time can lead to a dangerous build-up of calcium in the body which can weaken bones, and also damage the heart and kidneys.

Medics advise taking no more than 800 international units (IUs) per day.

Vitamin D is frequently sold in units called IU. One microgram of vitamin D is equal to 40 IU.