What Causes Low Level of Testosterone in the Body-TSHblog

Testosterone is the primary male sex hormone, though women produce it too in much smaller amounts. It supports fertility, muscle mass, bone density, and body hair, and low levels can cause real problems — fatigue, reduced muscle mass, low libido, and mood changes among them.

An important clarification: testosterone and hair loss

Since this article sits in our hair loss content, it’s worth being precise about something commonly misunderstood: low testosterone doesn’t cause hair loss, and higher testosterone doesn’t prevent it. Male pattern baldness (androgenetic alopecia) is driven by dihydrotestosterone (DHT), a hormone produced when the enzyme 5-alpha-reductase converts testosterone into DHT. Hair follicles that are genetically sensitive to DHT gradually shrink over time, regardless of whether total testosterone levels are high, low, or normal — it’s follicle sensitivity to DHT, not testosterone quantity, that determines pattern hair loss.

This has a practical implication: testosterone replacement therapy for genuinely low testosterone can, in some men who are genetically predisposed to pattern baldness, actually accelerate hair thinning, since more testosterone available for conversion means more DHT. This is a conversation to have directly with your doctor if you’re considering testosterone therapy and have a family history of pattern baldness — it doesn’t mean you shouldn’t pursue treatment for a genuine deficiency, but it’s a factor worth being aware of.

Prescription treatments that address hair loss directly (like finasteride, which blocks the conversion of testosterone to DHT) work on this pathway specifically, rather than on testosterone levels — which is why they’re effective for pattern hair loss regardless of whether a man’s testosterone is low, normal, or high.

What causes low testosterone

With that distinction clear, here are the factors associated with lower testosterone levels — relevant to overall health even if not directly tied to hair loss:

• Aging – testosterone naturally declines gradually after around age 30, though the rate varies significantly between individuals.
• Obesity – excess fat tissue converts testosterone into estrogen and reduces sex hormone-binding globulin (SHBG), the protein that carries testosterone in the blood. Weight loss can help restore levels in some men.
• Significant weight loss or very low body fat – can also suppress testosterone production, particularly when combined with inadequate nutrition.
• Chronic stress and poor sleep – both are associated with lower testosterone, likely via elevated cortisol and disrupted hormonal regulation.
• Sedentary lifestyle – lack of physical activity is associated with lower testosterone levels compared to an active lifestyle.
• Excessive alcohol use – can directly affect the testicular cells (Leydig cells) responsible for testosterone production.
• Diabetes and metabolic conditions – type 2 diabetes in particular is associated with lower testosterone levels.
• Certain medical treatments – chemotherapy can temporarily lower testosterone, usually recovering after treatment ends.
• Depression – low testosterone and depression are correlated in research, though the direction of cause and effect isn’t fully settled.

Supporting healthy testosterone levels

• Regular exercise, particularly resistance training, is associated with healthier testosterone levels, including in older men.
• Adequate protein intake supports muscle mass and overall metabolic health, both linked to healthier hormone levels.
• Stress management and consistent sleep help regulate cortisol, which in excess can suppress testosterone production.
• Correcting a vitamin D deficiency, if one is confirmed by a blood test, has been associated with modest improvements in testosterone levels in some studies — though this applies specifically to men who are actually deficient, not as a general boost for men with normal levels.

When to see a doctor

If you’re experiencing fatigue, low libido, mood changes, or reduced muscle mass alongside hair loss, a blood test can check your testosterone level and rule out or confirm a genuine deficiency. But treat hair loss and low testosterone as two separate things to discuss with your doctor — correcting one doesn’t reliably fix the other, and a dermatologist is the right specialist for evaluating hair loss specifically.