IGF-1 explained: growth hormone, muscle growth and the longevity trade-off

IGF-1 is the blood value that reflects your growth-hormone signal and is involved in muscle growth and recovery. At the same time the marker has a flip side: both a low and a high level are associated with long-term health downsides. So it is not a value where higher is automatically better.

I think IGF-1 is a fine example of a marker with two faces. What is good for your muscles at thirty is not necessarily good for your ageing afterwards.

What is IGF-1?

IGF-1 stands for insulin-like growth factor 1 and is the messenger through which growth hormone does much of its work. Your liver makes most of it in response to growth hormone, and it stimulates cell growth and repair in your muscles among other tissues. Your level depends on age, nutrition, sleep and training.

That is why IGF-1 says something about your anabolic status, your ability to build tissue.

IGF-1 and muscle growth

A healthy IGF-1 signal supports muscle repair and growth after training. It works together with other anabolic signals, such as testosterone, to build tissue. A low IGF-1 can hold back recovery and muscle building, certainly in older people.

A low level in older people is associated with higher mortality, which shows that too low is not desirable either (Sanders, 2018).

The flip side: IGF-1 and ageing

A high IGF-1 is not simply favourable, because it is also associated with long-term risk. Research describes a U-shaped relationship, where both low and high IGF-1 are linked with higher mortality (Rahmani, 2022). The idea of antagonistic pleiotropy captures this well: what helps you grow young can make you more vulnerable when old (Zhang, 2021).

When and how do you test IGF-1?

IGF-1 is interesting if you want to track your recovery, your anabolic status or your longevity strategy. It is a simple blood value measured at rest, independent of a single meal. Always read your value in the context of your age, because IGF-1 naturally declines over the years.

To track IGF-1 alongside your other markers, compose a panel through our custom blood test. See also the overview measuring metabolic health and blood values for strength athletes.

My advice: do not blindly chase a high IGF-1. Aim for a healthy middle and discuss a strongly abnormal value with your GP.

References

1. Rahmani J, Montesanto A, Giovannucci E, et al. Association between IGF-1 levels ranges and all-cause mortality: a meta-analysis. Aging Cell. 2022. PMID: 35048526.
2. Sanders JL, Guo W, O'Meara ES, et al. Trajectories of IGF-I predict mortality in older adults: the Cardiovascular Health Study. Journal of Gerontology A Biological Sciences and Medical Sciences. 2018. PMID: 28977343.
3. Zhang WB, Ye K, Barzilai N, et al. The antagonistic pleiotropy of insulin-like growth factor 1. Aging Cell. 2021. PMID: 34363732.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. A blood test is a tool to walk into the conversation with your GP better informed, not a diagnosis in itself. For treatment decisions, discuss your results with your GP.