FSH is released by the pituitary gland alongside luteinising hormone (LH). While LH tells the testes to make testosterone, FSH acts on the Sertoli cells, the nurse cells that support developing sperm through the long process of spermatogenesis.
Like LH, FSH sits in a feedback loop. The Sertoli cells release a hormone called inhibin B that tells the pituitary to ease off. When sperm production is healthy, inhibin B is high and FSH stays modest. When it falters, inhibin B drops and FSH climbs.
The name comes from its role in women, where it ripens egg follicles. In men it is one of the most useful blood tests in a fertility work-up, usually read alongside a semen analysis.
What does FSH do in men?
FSH supports the Sertoli cells, which nurture sperm as they develop. Together with high testosterone levels inside the testes, it keeps sperm production running.
Sperm take many weeks to develop, so any change in FSH signalling shows up in the semen only weeks later. Our piece on how long it takes sperm to regenerate walks through that timeline.
Because FSH and LH come from the same gland and answer to the same signal from the brain, they often move together. But FSH is tuned to the sperm-making side of the testes and LH to the testosterone-making side, so a man can have a raised FSH alongside perfectly normal testosterone.
What does a high FSH level mean?
A high FSH usually means the testes are not making sperm efficiently and the pituitary is turning up the volume. In a study of 349 young Danish men, higher FSH went with lower sperm concentration.1
In that study, every man whose FSH was above 10 IU/L and whose inhibin B was below 80 pg/mL had a sperm concentration under 20 million per millilitre.1 That does not make FSH a replacement for a semen test, but it is a strong clue. Causes of raised FSH range from past testicular injury or infection to genetic conditions, and some men with azoospermia have high FSH.
What does a low FSH level mean?
A low FSH points to the pituitary or hypothalamus not sending the signal. One of the most common modern causes is testosterone or anabolic steroids taken from outside the body, which switch off FSH and sperm production.3
That shutdown is reversible for most men. Pooled data from 1,549 healthy men in hormonal contraception studies found that after stopping, sperm counts recovered to 20 million per millilitre in 67% within six months, 90% within 12 months and all men within 24 months.3 Those were healthy volunteers on planned regimens, so recovery after years of unsupervised steroid use may be slower.
Can FSH treatment improve fertility?
It depends on why FSH is abnormal. European urology guidelines say hormone stimulation for men with high FSH or normal hormones is controversial and should not be used outside clinical trials.2
Men whose FSH is low because of a genuine pituitary or hypothalamic problem are a different case, and a specialist can discuss options. Either way, lifestyle factors still matter for sperm quality; see our guide to lifestyle factors that affect male fertility. If you have been trying to conceive for a year without success, ask your GP about a semen analysis and hormone tests.
Common questions
Is FSH tested in a male fertility work-up?
Often, yes, particularly when the semen analysis shows a low sperm count or no sperm. It helps distinguish a testicular problem from a pituitary one.1
Does FSH rise with age in men?
Yes, gradually. Pituitary gonadotropins, including FSH, rose over time within the same men in the Massachusetts Male Aging Study.4
Can lifestyle changes lower a high FSH?
FSH is a signal rather than the problem itself, so the aim is to protect and support sperm production rather than chase the number. Stopping any testosterone or steroid use, not smoking and keeping a healthy weight are sensible steps, but a specialist should interpret a persistently abnormal result.
Read more on this
How long does it take sperm to regenerate?
Lifestyle factors that affect male fertility: a practical guide
Sources
- Jensen TK, et al. Inhibin B as a serum marker of spermatogenesis: correlation to differences in sperm concentration and follicle-stimulating hormone levels. A study of 349 Danish men. J Clin Endocrinol Metab. 1997;82(12):4059-4063. PubMed
- Minhas S, et al. European Association of Urology guidelines on male sexual and reproductive health: 2021 update on male infertility. Eur Urol. 2021;80(5):603-620. PubMed
- Liu PY, et al. Rate, extent, and modifiers of spermatogenic recovery after hormonal male contraception: an integrated analysis. Lancet. 2006;367(9520):1412-1420. PubMed
- Feldman HA, et al. Age trends in the level of serum testosterone and other hormones in middle-aged men: longitudinal results from the Massachusetts Male Aging Study. J Clin Endocrinol Metab. 2002;87(2):589-598. PubMed
Not medical advice. Written by Eric Stephens from the research cited above; not reviewed by a doctor. If something worries you, see a GP.