Is low SHBG associated with increased cardiometabolic risk in men?

Sex hormone-binding globulin (SHBG) is increasingly recognized not merely as a carrier protein for sex steroids, but as a significant metabolic marker. In men, low levels of SHBG are consistently linked to a heightened risk of developing a range of cardiometabolic conditions, often independent of total testosterone levels.

Clinical and effectiveness evidence

Prospective studies and cross-sectional data indicate that SHBG is a robust predictor of cardiovascular and metabolic health outcomes in men:

• Hypertension and Coronary Disease: Higher levels of SHBG are inversely associated with the development of hypertension, with an odds ratio (OR) of 0.74 per standard deviation increase. Low levels are similarly associated with increased risks of coronary heart disease.
• Metabolic Syndrome: Men in the lowest quartile of SHBG concentrations face significantly higher odds of metabolic syndrome (OR 2.17). This relationship is particularly strong regarding dyslipidemia, specifically hypertriglyceridemia and low HDL cholesterol.
• Diabetes Risk: Low SHBG is a strong, independent predictor of type 2 diabetes. Large-scale genetic data, including Mendelian randomization studies, suggest that SHBG may have a causal role in the development of glucose intolerance and insulin resistance.

Mechanistic explanations

The link between SHBG and cardiometabolic risk is driven by complex hepatic and endocrine pathways:

• Hepatic Synthesis Suppression: High levels of insulin and proinflammatory cytokines, often resulting from visceral adiposity, suppress the hepatic production of SHBG. Consequently, low SHBG often serves as a proxy for liver fat accumulation and systemic insulin resistance.
• Hormonal Bioavailability: SHBG regulates the fraction of free, biologically active testosterone. While the association between SHBG and metabolic risk remains significant even after adjusting for testosterone, the interplay between these hormones suggests that SHBG levels reflect the broader androgenic and metabolic environment of the body.
• Causal Markers: Genetic evidence supports the "causal marker" hypothesis, where low SHBG is not just a symptom of metabolic dysfunction but a potential contributor to the pathophysiology of insulin resistance.

Bottom line

Low SHBG is a robust, independent indicator of increased cardiometabolic risk and metabolic syndrome in men. It serves as a valuable clinical marker for predicting future hypertension and type 2 diabetes, often reflecting underlying insulin resistance and hepatic metabolic stress.