Browse evidence-based analysis of health-related claims and assertions
Being tall or short doesn’t change how much vitamin D is in your blood—any link you see is probably because something else, like how much time people spend outside, is affecting both height and vitamin D levels.
Causal
People who naturally have more vitamin D in their blood tend to be a tiny bit taller as adults—like a small nudge in height—because their bodies have had more vitamin D throughout life.
Correlational
Taking a high-dose vitamin D pill every day for three months won't help young men who are low on vitamin D get stronger from weight training—and might even make them weaker compared to those who take a sugar pill.
If you're a young man with low vitamin D and you lift weights, your muscles will get stronger and you'll gain more muscle mass—even if you don't take vitamin D pills.
Taking a daily vitamin D pill of 8000 IU for 3 months can boost vitamin D levels in young men from dangerously low to healthy levels, while those who take a fake pill (placebo) stay low.
If young men who don’t have enough vitamin D take a high-dose vitamin D pill every day for 12 weeks while working out, they lose belly fat — but if they take a fake pill instead, their belly fat doesn’t change.
Taking a high-dose vitamin D pill every day for three months won't help young men who are low on vitamin D build more muscle or gain more lean body mass from weight training, even though their vitamin D levels go up to normal.
Even if the levels of calcium, magnesium, and phosphate in the mice’s bodies were kept the same, removing the vitamin D receptor or not giving them enough vitamin D still changed their muscle strength and which genes were active.
Mechanistic
When scientists remove the vitamin D receptor in mice, the genes that help muscles grow and repair don't work right anymore, which might mess up how their muscles heal or develop.
When mice don’t have enough vitamin D or can’t use it properly, their muscles weaken because the genes that help move calcium around in muscle cells don’t work as well.
When mice don’t get enough vitamin D from their diet, their muscles start breaking down more because certain proteins that signal muscle loss become more active.
When mice can't use vitamin D properly, their muscles get weaker, their muscle fibers shrink, and a protein that stops muscle growth increases—so vitamin D seems to help keep muscles strong and healthy.
Being tall doesn’t make your vitamin D levels lower — it just looks that way because taller people might spend less time in the sun, weigh more, or have different lifestyles that affect vitamin D. The real cause isn’t height itself.
People with certain inherited gene differences that affect how their body uses vitamin D tend to be taller or shorter as adults, which suggests that having the right amount of vitamin D over a lifetime might help bones grow better than taking vitamin D pills for a short time.
If you already have enough vitamin D, taking more won’t make you significantly taller — the tiny boost you might see is too small to matter in real life.
Quantitative
Being taller doesn’t cause your body to have more or less vitamin D—any link you see between height and vitamin D is probably because taller people spend more time outside or have bigger bodies, not because height directly affects vitamin D.
People who naturally have more vitamin D in their blood tend to be a tiny bit taller as adults—like a small nudge in height—not much, but it’s a real pattern scientists noticed.
When older men take vitamin D pills while doing weight training, their bodies might slow down the production of a specific enzyme because they have too much vitamin D in their blood — like a safety switch turning itself off.
Taking vitamin D pills while doing weight training doesn’t change the levels of a specific protein in your muscles that helps vitamin D work, which means vitamin D probably isn’t helping your muscles grow by using this protein.
Doing strength training for 12 weeks can make your thigh muscles bigger and stronger, whether you're young or old—but taking vitamin D pills won’t make that improvement any better.
When older men lift weights for 12 weeks and take a daily vitamin D3 pill, their muscles get stronger relative to their size compared to men who only take calcium — even though their muscles don’t get bigger or stronger in absolute terms.
Taking a daily vitamin D3 supplement while doing strength training might help young men build more of a certain type of muscle fiber and reduce a protein that limits muscle growth, compared to just taking calcium.
Men who had excess belly fat saw their vitamin D levels go up by 27% after a year of eating better and moving more—even though they didn’t take any vitamin D pills or supplements.
If a man with excess belly fat eats less and moves more for a year, his belly fat, hunger hormone levels, and vitamin D levels all get better.