Sex hormone binding globulin (SHBG) is a protein made by the liver which binds tightly to the sex hormones: testosterone, dihydrotestosterone and oestradiol. SHBG transports these hormones around the body in the blood. Bound hormones are biologically inactive. The levels of SHBG are used to give a good indication of the overall amount of active testosterone that is available in the blood.
Sex hormone binding globulin binds to the sex hormones testosterone and oestradiol and in do doing so decreases their biological activities. In other words, when the hormones are attached to SHBG they are inactive. The secretion of SHBG is stimulated by oestrogens and suppressed by androgens which causes a difference in concentration between genders. Although SHBG binds to both oestradiol and testosterone, it has a greater affinity with the latter.
The measurement of SHBG can be used to indicate how much testosterone is available for use by the body. The amount of testosterone bound to SHBG in men and women differs. In men around 45% and in women approximately 70% of testosterone is tightly bound to SHBG. The rest is mostly bound weakly and reversibly to albumin. Up to 3% is unbound and freely available to tissues in the body.
High levels of SHBG are usually witnessed in elderly men and patients who have an underactive thyroid or who have liver cirrhosis. Levels can also be raised in women who take the contraceptive pill or in those who take antiepileptic medication. When levels of SHBG are increased, the level of testosterone available to the tissues may be reduced. This can lead to a reduced libido and energy levels in men.
Decreased levels of SHBG may indicate there is a greater amount of free testosterone in circulation. As more total testosterone is available to the body it can cause Polycystic Ovary Syndrome (PCOS) in women. The condition affects how the ovaries work and can cause unwanted side effects. Symptoms of PCOS include:
PCOS affects 1 in 5 women who are of reproductive age and can have some psychological side effects, like:
The condition is chronic and usually first manifests in a female’s teenage years. The condition can also result in infertility which can also lead to psychological symptoms.
Some of the symptoms of PCOS can be controlled with lifestyle changes, medication and cosmetic measures.
Eating the right diet can help to control some of the symptoms and risks associated with PCOS. Heart disease and diabetes are side effects of PCOS and so you should incorporate an increased amount of fruit and vegetables into your diet, eat lean meat rather than fatty versions and limit the amount of sugary and fatty foods you eat. Making small changes such as swapping full-fat dairy for low-fat equivalents can help to make a difference.
Eat a diet which has a low glycaemic index may also be beneficial. Low GI diets incorporate foods which cause your blood sugar to rise slowly can reduce the symptoms of PCOS. Foods include:
Low GI diets and foods may help to alleviate the symptoms of PCOS because many women who have the condition are resistant to insulin. Insulin is a hormone which helps the body to use the energy from food.
High levels of SHBG and thus low testosterone has been associated with low protein intake. Insulin is associated with SHBG levels. Protein intake has been shown to increase insulin levels and insulin has been shown to decrease SHBG levels which in turn can increase the amount of testosterone.
Being overweight can also increase the severity of the symptoms associated with PCOS. Physical activity can help with weight loss but perhaps, more importantly, it can improve the body’s response to insulin.
Weight loss in PCOS patients is also beneficial in all other symptoms of the condition. Exercise should be encouraged and a plan should be devised with your GP.
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