Vitamin D pills left the growth factor IGF-1 untouched

IGF-1 sits near the centre of the body's growth signalling, influencing muscle, bone and metabolism, and it features prominently in debates about both anabolism and ageing. Vitamin D, meanwhile, is one of the most widely taken supplements in the world, and there has been genuine equivocality about whether the two interact. If swallowing vitamin D reliably raised circulating IGF-1, that would matter to lifters chasing growth and to longevity enthusiasts trying to keep the marker low alike. This review pooled the randomised trials to find out whether any such effect actually exists in people.

The authors searched PubMed, Scopus and ISI Web of Science up to May 2019 for randomised controlled trials that tested vitamin D supplementation against a control condition and measured serum IGF-1. Six trials qualified, with 773 participants between them. Mean changes in IGF-1 in each treatment group were pooled using a random-effects model. Risk of bias in the included trials was assessed with the Cochrane scale, and the overall quality of the evidence was evaluated using the NutriGrade approach.

Compared with control, vitamin D supplementation had no significant effect on serum IGF-1. The pooled difference was 4.66 ng/ml, and the uncertainty around it spanned both a decrease and an increase, so the result is consistent with no effect at all. Subgroup analyses likewise found no meaningful changes anywhere. The included trials disagreed with each other considerably, which the authors acknowledge, and they conclude that the evidence does not convincingly show any clinically relevant effect of vitamin D on IGF-1.

This pushes back on the idea that vitamin D meaningfully drives the growth factor side of the hormonal picture, an idea that circulates in both supplement marketing and longevity discussion. At the same time, the authors are careful: only six trials existed to pool, their quality varied, and they call for more high-quality studies before a consensual conclusion can be reached. The review neither supports an effect nor definitively closes the door on one in particular populations or doses.

If you take vitamin D hoping to move IGF-1 in either direction, this pooled evidence gives you no reason to expect it will. That is useful knowledge in a supplement landscape where hormonal claims are common and rarely tested this directly. Vitamin D's other roles, from bone to immune function, were not the subject of this review, so nothing here speaks for or against supplementing on those grounds.