Go from Flabby to Fit with this Common Vitamin

By Dr. Scott Olson, ND Posted June 27, 2025

If you’re like many of us, you woke up one day, looked in the mirror, and realized you’re no spring chicken anymore.

Even worse—when you weren’t paying attention—it seems you somehow misplaced the muscles of your youth and have gone from fit to flabby.

Aging has a way of humbling us like that.

But scientists say a surprising nutrient could be key to rebuilding your muscles…

A fascinating preprint study found that an everyday vitamin D supplement helps your body direct excess calories toward building muscle instead of storing them as fat.

We’ve known that vitamin D is crucial for bone health. But researchers are now uncovering its critical role in body composition.

With up to 50 percent of adults having insufficient vitamin D levels—and seniors being at a substantially higher risk for D deficiency—chances are good that your levels are too low.

However, the study found that high doses of the so-called sunshine vitamin encourage the body to prioritize muscle growth over fat storage. And we can harness that knowledge to help us maximize the benefits of our muscle-building efforts.

The body’s decision of whether to store energy as fat or use it to build muscle is influenced by two critical hormones: leptin and myostatin.

Leptin is produced by fat cells and acts as a signal to tell us when we’re “full”—the more fat you have, the more leptin you produce. Myostatin, on the other hand, is made by muscles and functions as a brake on muscle growth.

According to the study, your body is more likely to use nutrients for muscle growth and repair when it senses high leptin and low myostatin levels.

Resistance training naturally helps lower myostatin temporarily—which explains why weight lifting promotes muscle gains.

However, vitamin D also plays a significant role in this process:

• Improves leptin sensitivity so your body responds better to existing leptin signals
• Reduces myostatin production to remove some natural limitations on muscle growth
• Directs more calories toward muscle rather than fat storage

The study’s results were impressive: participants receiving high doses of vitamin D gained significantly more strength and muscle without accumulating extra fat compared to the control group.

This suggests that combining vitamin D supplements with resistance training is an effective way to build more muscle while minimizing fat gain.

If you’re interested in seeing how vitamin D could help you go from flabby to fit, ask your doctor about getting your levels tested and whether supplements are right for you.

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P.S. Drive-thru disaster hits fast forward on aging!

Source:

Roizen J, Long C, Casella A, Nguyen M, Danahy L, Seiler C, Lei M, Mark J. High dose dietary vitamin D allocates surplus calories to muscle and growth instead of fat via modulation of myostatin and leptin signaling. Res Sq [Preprint]. 2024 May 8:rs.3.rs-4202165. doi: 10.21203/rs.3.rs-4202165/v1. PMID: 38766160; PMCID: PMC11100886.