Causes of Elevated SHBG in a 66-Year-Old Male with Normal Weight, Liver Function, and Thyroid
In a 66-year-old man with normal weight, normal liver function, and normal thyroid, the most likely cause of elevated SHBG is aging itself, followed by medication effects (particularly anticonvulsants, estrogens, or thyroid hormone), smoking, or HIV/AIDS. 1
Primary Causes to Consider
Age-Related Elevation
Aging is a well-established independent cause of elevated SHBG and is likely the primary explanation in this patient. 1 Research demonstrates that SHBG levels increase progressively with age due to increased hepatic synthesis—specifically, aging increases hepatic nuclear factor 4α (HNF-4α), which promotes SHBG production, while simultaneously decreasing PPAR-γ and COUP-TF, which normally inhibit SHBG synthesis. 2 This age-related increase occurs even when controlling for other factors like body mass index and insulin levels. 3
Medication-Induced Elevation
The 2025 European Association of Urology guidelines explicitly list drugs as the first category of SHBG elevation: 1
- Anticonvulsants (phenytoin, carbamazepine)
- Estrogens (including topical preparations)
- Thyroid hormone (even if TSH is normal, exogenous thyroid hormone increases SHBG)
A thorough medication review is essential, including over-the-counter supplements and topical preparations that the patient may not consider "medications."
Smoking
Smoking is independently associated with elevated SHBG levels. 1 This is often overlooked but represents a modifiable factor. Interestingly, smoking also correlates with higher free testosterone levels in healthy men. 3
HIV/AIDS
HIV infection causes elevated SHBG independent of other factors. 1 While less common in this age group without known risk factors, HIV testing should be considered if other causes are excluded, particularly given the clinical implications.
Excluded Causes (Based on Normal Labs)
Since liver function and thyroid are normal, you can exclude:
- Hepatic disease (cirrhosis, hepatitis) - would show abnormal liver enzymes 1, 4
- Hyperthyroidism - would show suppressed TSH 1, 4
Since the patient has normal weight, you can largely exclude:
- Obesity-related causes - obesity actually decreases SHBG 1
Diagnostic Approach
Obtain a detailed history focusing on:
- Complete medication list including supplements, topical preparations, and herbal products
- Smoking history (current or recent)
- HIV risk factors and consider testing
- Dietary patterns - specifically protein and fiber intake, as low protein diets can elevate SHBG 5
- Symptoms of hypogonadism - reduced libido, erectile dysfunction, decreased energy 1
Measure free or bioavailable testosterone if not already done, as elevated SHBG can mask true androgen deficiency by lowering free testosterone despite normal total testosterone. 4 The Endocrine Society recommends measuring free testosterone when SHBG is altered. 4
Clinical Pitfalls
Common mistake: Assuming normal total testosterone means no hypogonadism when SHBG is elevated. The elevated SHBG binds more testosterone, reducing bioavailable hormone despite normal total levels. 4
Important caveat: While aging increases SHBG, this doesn't mean it's benign—the resulting decrease in bioavailable testosterone can contribute to sexual dysfunction, decreased muscle mass, reduced bone density, and decreased red cell mass. 5 The clinical significance depends on whether the patient has symptoms of androgen deficiency.
Nutritional Considerations
Dietary factors influence SHBG: 5
- High fiber intake increases SHBG
- High protein intake decreases SHBG
- Total calories, fat, and carbohydrate intake do not significantly affect SHBG
If the patient follows a low-protein, high-fiber diet (common in health-conscious elderly men), this could contribute to elevated SHBG and decreased testosterone bioactivity. 5