SHBG

SHBG is a protein your liver makes and that binds testosterone and oestradiol in your blood. As long as a hormone is attached to it, it is in transit and not available; only the free part can enter the cell. SHBG is therefore the regulator of how much of your sex hormones is active: at the same total testosterone a high SHBG leaves little free and a low SHBG plenty. How much SHBG your liver makes depends on what is happening in your body. Insulin suppresses production, which is why SHBG falls with belly fat, insulin resistance and a fatty liver, often years before blood sugar moves. Oestrogen and thyroid hormone drive production, which is why SHBG rises on the pill, in pregnancy and with an overactive thyroid. It also rises with age, especially in men, and with eating too little or a low body weight. Your report shows SHBG in nmol/L, with one range for men and one for women: women sit about twice as high, because oestrogen drives production. Normal is 18 to 54 nmol/L in a man of 19 to 49 years and 32 to 128 nmol/L in a woman of 19 to 47 years, where the labs overlap.

SHBG is worth knowing for two reasons, and the first has nothing to do with hormones. A low SHBG is one of the earliest signs of insulin resistance: the liver makes less SHBG as soon as it sees too much insulin and too much fat, and that happens long before fasting glucose or HbA1c moves. A low SHBG in a man with belly fat or a woman with PCOS is therefore not a hormone problem but a metabolic signal, and one of the better predictors of type 2 diabetes to be found on an ordinary report. The second reason is reading testosterone. Without SHBG a total testosterone can only be half read. A man with excess weight often has a low total testosterone and a low SHBG, so the free part is better than it looks; an older man or a man with an overactive thyroid has a normal total with a high SHBG, so the free part is worse than it looks. In women with PCOS a low SHBG is precisely the reason a normal total testosterone still yields too much active androgen, with excess hair growth and acne as the result. That is why SHBG belongs with every testosterone test, and why they move in opposite directions with weight loss: SHBG rises and free testosterone is thereby distributed more healthily.

A low SHBG means, first of all, too much insulin: belly fat, insulin resistance, a fatty liver, and in women PCOS. Beyond that an underactive thyroid, prednisone, growth hormone and anabolic steroids, and in women some progestogens. The result is more free testosterone at the same total: in men that masks a low total, in women it amplifies the androgenic complaints. A high SHBG usually means oestrogen or thyroid hormone: the pill, hormone therapy, pregnancy, an overactive thyroid. It also rises with age, especially in men over fifty, with eating too little and a low body weight, and with serious liver disease. The result is less free testosterone at the same total: a normal total with complaints of too little testosterone in an older man is often a high SHBG. The lever with a low SHBG is that of insulin resistance, and it works: losing weight around the middle, less sugar, soft drinks and fast carbohydrates, and daily movement let SHBG rise within months. It is one of the few hormone values you can improve under your own steam, and it is also the proof that the lifestyle change is landing. A high SHBG from the pill or age is not something to lower; there free testosterone is the value to look at. Always read SHBG beside total testosterone, and have free testosterone or the FAI calculated. With a low SHBG a look at triglycerides, fasting glucose and the liver values belongs too, because they tell the same story from the other side.