SHBG blood level: training, metabolism and testosterone

SHBG is a protein, and its full name explains the job. That name is sex hormone binding globulin, in Dutch geslachtshormoonbindend globuline. This binding globulin holds testosterone and oestradiol, the first tightly and the second more loosely.

Hormone attached to SHBG cannot enter the cell. SHBG is therefore not a sex hormone itself, only the transport layer around them.

For you as an athlete that distinction is practical. Your muscle and bone tissue responds to the free fraction, not to the total. A panel measuring only total testosterone leaves that split unanswered.

Only with SHBG alongside can free testosterone be calculated. That is the value driving your training adaptation.

SHBG is reported in nanomoles per litre (nmol/l). The reference values below are split by sex and by age band.

Those age bands are not a formality. In men SHBG rises with the years, and the ceiling moves from 54.1 to 76.7 nmol/l. A man of sixty at 70 nmol/l therefore sits inside his own band.

Read the same result against the younger band and it looks wrongly raised. The floor shifts just as much, because his band only starts at 20.6 nmol/l.

Reference values also differ per laboratory and per analyser. Your sample is analysed within a network of independent, certified laboratories. They do not all run the same instrument.

For SHBG that produces several different reference bands. So always use the band printed on your own laboratory report.

This is the heart of the page, and for you it runs both ways. SHBG moves in two directions, depending on where your body sits. A strict cut and a thickening waist push the value opposite ways. Both hand you a total testosterone that reads differently from what it is.

What pushes SHBG down is mainly metabolic. Excess weight and insulin resistance are the dominant cause, through chronically raised insulin. Type 2 diabetes, an underactive thyroid, glucocorticoids and fatty liver disease lower it too.

Androgens and anabolic steroids suppress SHBG as well, and that effect is large. With a low SHBG the total falls with it, while the free fraction stays normal. Your result then looks poor without the available hormone having dropped.

The other direction is more common in athletes than expected. Ageing, an overactive thyroid, liver cirrhosis and some anti-epileptic drugs raise SHBG. Oral oestrogens do the same, including the combined pill and oral HRT; transdermal delivery does not.

For you the most important route is energy. Anorexia and severe energy restriction clearly raise SHBG, and prolonged low energy availability works the same way. Combine a long endurance block with a strict deficit and SHBG climbs.

The total then holds up nicely, while free testosterone drains away underneath. That is exactly the scenario in which a panel reassures you without cause.

SHBG is also a signal in its own right, not merely a correction factor. A low SHBG is associated with a higher risk of type 2 diabetes in adults. That comes from large prospective cohorts and from Mendelian randomisation studies, in both sexes.

It is an association across groups, not a prediction about you. A low value is mainly a reason to weigh your metabolic health seriously.

In practice SHBG belongs on the same request as total testosterone. Your free testosterone comes out of that pair, not out of either value alone. Measuring total alone in an athlete carrying visceral fat produces a misleading result fast.

The same holds for someone deep into a cut. A testosterone test puts the values side by side in one draw.

Measure SHBG together with testosterone, never as a standalone test. The result is a ratio, and without a total it says little. A free testosterone test collects both values in a single draw.

Timing matters. Testosterone follows a daily rhythm peaking in the early morning. Draw fasting in the morning, and keep the same window when you repeat it. SHBG itself varies far less across the day, but the pair must stay comparable.

A few moments make this measurement genuinely worth taking. At the start or end of a strict diet, when strength and recovery fade. During a long endurance block where weight drops and form does not follow.

With a growing waist, where insulin resistance is the likeliest explanation. And when an earlier total testosterone came back low or surprisingly high.

With an unclear picture, add DHT or inhibin B, depending on your question. Do not measure straight after an exhausting session or a race. Schedule the draw on a rest day, at the end of an easy week. If you repeat it later in the season, pick the same phase of your training week.