Men's libido and ED in midlife

When function is intact but desire has dropped — what changes, what to test, what to read.

The pattern most men over 45 do not bring up at the annual physical: function works fine when it needs to, but the underlying interest level has dropped. It is not zero. It is just lower than it used to be, and it has been creeping down for a while.

What changes biologically

Three things move together after 40 in most men. Total testosterone trends down at roughly 1% per year past age 30 (Massachusetts Male Aging Study). SHBG goes up, which means free T (the actually bioavailable fraction) drops faster than total T. DHEA-S, the adrenal androgen precursor, drops faster than either.

Behavioural and lifestyle factors stack on top: sleep quality drops (Ohayon 2004), visceral adiposity increases aromatase activity (converting more T to estradiol), chronic stress elevates SHBG further, alcohol after 6pm tanks overnight T production.

Function vs desire

This matters: erectile function is mostly a vascular question. Erectile desire is mostly a hormonal-and-neural question. The same man can have intact function and low desire, or vice versa. They are not the same problem and they do not respond to the same intervention.

The bloodwork to request

• Total testosterone, ideally before 10am (diurnal variation is real)
• Free testosterone (calculated or direct)
• SHBG
• Estradiol (sensitive assay, not the standard one)
• DHEA-S
• Prolactin
• LH and FSH (to distinguish primary vs secondary hypogonadism)
• TSH and free T4 (thyroid affects both libido and function)
• Fasting glucose + HbA1c + fasting insulin

What moves the needle before considering TRT

• Strength training, 3x/week, compound lifts — reliably raises free T 10-20% in observational studies
• Sleep architecture — fix the 2-4am wakeups; T production is overnight
• Alcohol off by dinner
• Visceral fat reduction — lowers aromatase activity, lowers SHBG
• Vitamin D if deficient (under 30 ng/mL)

If after 6 months of full effort on those, free T is still in the bottom quintile for your age and symptoms persist, the TRT conversation becomes reasonable. Read TRT after 40 — the honest take before that appointment.