How body weight influences the effectiveness of vitamin D supplements

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Let’s talk about a recent health study. It was part of a bigger research project called the Vitamin D and Omega-3 Trial (VITAL).

Here, they looked at the effects of vitamin D supplements on our health. They wanted to see if the supplements made a difference to people of different sizes.

Why Did They Do This Study?

VITAL found that vitamin D supplements seemed to help people who had a normal weight. But it didn’t seem to help people who were heavier.

This raised a question – does a person’s weight affect how vitamin D supplements work in the body?

What Were They Looking For?

To answer this, the researchers looked at whether a person’s body mass index (BMI) changes how vitamin D works in their body.

BMI is a measure that helps us understand if a person has a healthy body weight for their height.

How Was the Study Done?

The original VITAL study was a big experiment. People were randomly picked to take either a vitamin D supplement or a placebo (a pill with no medicine).

This way, the effects of vitamin D could be compared to no treatment.

This new research analyzed a smaller group from the larger VITAL study. These people had given a blood sample at the start of the VITAL study and again two years later.

The researchers checked these blood samples for different things related to vitamin D.

What Did They Measure?

They measured different things in the blood that can tell us about vitamin D in the body.

These included total vitamin D levels (25-OHD), free vitamin D (FVD), bioavailable vitamin D (BioD), and vitamin D-binding protein (VDBP).

They also looked at albumin, parathyroid hormone (PTH), and calcium levels.

What Did They Find Out?

The researchers found that people who weighed more had lower levels of most of the things they measured, like total vitamin D, free vitamin D, bioavailable vitamin D, and calcium.

They had higher levels of parathyroid hormone.

When they looked at the people who took the vitamin D supplement, they found that their vitamin D levels did increase over the two years.

But this increase was smaller in people who weighed more. The supplement didn’t really change the other measures like albumin, PTH, or calcium levels.

What Does This Mean?

These findings suggest that a person’s weight can change how their body responds to vitamin D supplements.

This could help explain why the VITAL study found that vitamin D supplements helped people of normal weight more than those who were heavier.

It also suggests that doctors might need to think about a person’s weight when considering vitamin D supplements.


In simple terms, the study shows that weight matters when it comes to vitamin D supplements. If you’re heavier, your body may not respond as well to these supplements.

More research is needed, but this could be a big step forward in understanding how to better use vitamin D supplements for everyone’s health.

The research was published in JAMA Network Open.

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