Testosterone After 40: How to Maintain Optimal Levels as You Age

Turning 40 does not mean your best years are behind you. But your body is changing, and so is your hormonal picture. Testosterone, a hormone involved in energy, muscle, libido and mood, tends to drift lower with age, and many men wonder how much of that is inevitable. The research suggests it is a gradual slope rather than a cliff, and that part of it is linked to factors you can influence.

This guide covers what studies show about testosterone after 40, the lifestyle factors most closely linked to it, what is known (and not known) about prostate health and testosterone therapy, and when to talk to a doctor.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Thrive is a wellness app, not a medical device. Always consult a qualified healthcare provider before making changes to your health regimen or starting any hormone therapy.

What Actually Happens to Testosterone After 40

In the Massachusetts Male Aging Study, a population-based cohort of men aged 40 to 70 followed for 7 to 10 years, total testosterone declined 0.8 percent per year when comparing men of different ages and 1.6 percent per year within the same men over time. Free testosterone fell about 2 percent per year in the cross-sectional comparison and bioavailable testosterone 2 to 3 percent per year over follow-up.^[1] Sex hormone-binding globulin (SHBG), the protein that binds testosterone, rose about 1.6 percent per year, which tends to reduce the share of testosterone that is free.^[1] Our guide to free testosterone vs total testosterone explains how each is measured. See also our testosterone levels by age guide and our testosterone after 50 guide.

Those are averages, and individual men differ widely. The same study found that apparent good health (no chronic illness, medication use, obesity or heavy drinking) was associated with 10 to 15 percent higher levels of several androgens, and the authors suggested that new poor health may accelerate the age-related decline.^[1] In the European Male Aging Study of 3,200 men aged 40 to 79, age was linked to lower free testosterone with signs of reduced testicular function, while obesity and comorbidity were linked to lower testosterone through different pathways.^[2] In other words, age matters, but health status and body weight matter too.

Lower testosterone can contribute to symptoms such as low energy, low libido and reduced muscle, but these also have many other causes, including poor sleep, stress, depression, medications and other medical conditions. That is why symptoms are a reason to see a doctor, not a reason to self-diagnose.

Lifestyle Factors Linked to Testosterone in Men Over 40

Lifestyle will not stop aging, but several factors are associated with where men sit within the normal range. None of the following is a guaranteed way to raise your own level.

Body Weight and Composition

In the European Male Aging Study, men with a BMI between 25 and 30 had total testosterone about 2.3 nmol/L lower, and men with a BMI of 30 or more about 5.1 nmol/L lower, than men with a BMI under 25. The pattern pointed to the hypothalamus and pituitary rather than the testes as the site of the change.^[2] Fat tissue also contains aromatase, an enzyme that converts testosterone to estrogen, which is one proposed contributor.

The encouraging part is that this association appears reversible. A meta-analysis of 24 studies found both low-calorie diets and bariatric surgery were associated with increases in total and free testosterone, averaging about 2.9 nmol/L with diet and 8.7 nmol/L with surgery, and the degree of weight loss was the best predictor of the rise.^[3] These were men with obesity; results will be smaller for men near a healthy weight.

Resistance Training

Resistance training helps preserve muscle, bone density and insulin sensitivity as you age, which supports healthy aging whatever it does to testosterone itself. The best exercises for testosterone are mostly the same compound lifts as at 25, but recovery needs often rise with age, so allow more rest between hard sessions and pay attention to mobility and injury prevention.

Sleep

In a controlled study, ten healthy young men (average age 24) who slept 5 hours a night for one week had daytime testosterone 10 to 15 percent lower than during normal sleep.^[6] A later randomized inpatient study in young men found no significant drop in testosterone with sleep restriction, so the evidence is mixed.^[7] Sleep often changes with age, so protecting it matters. Consistent timing, a dark cool room and limiting late-night screens are sensible starting points. See our sleep and testosterone guide.

Stress Management

By 40 many men carry heavy career and family responsibilities. Experiments show that raising cortisol can lower testosterone in the short term, but the effect of everyday psychological stress is less clear. Our article on stress, cortisol and testosterone covers what is and is not established.

A Sample Day for Men Over 40

This is a general healthy-routine template, not a testosterone protocol. Adjust it to your schedule and any medical advice you have received.

Nutrition Priorities After 40

Protein

A meta-analysis of 49 trials found that protein supplementation enhanced muscle and strength gains from resistance training, that its benefit was smaller with increasing age, and that intakes above about 1.6 g per kg of body weight per day added no further gain in fat-free mass.^[8] A separate analysis of men around 71 versus 22 years old found older men needed a larger relative protein dose in a single meal (about 0.40 versus 0.24 g per kg) to maximally stimulate muscle protein synthesis,^[9] so spreading protein across meals is a reasonable approach. Note that the older men in that analysis were roughly three decades older than a typical 40-year-old. See our testosterone-supportive foods and our guide to zinc and magnesium.

Vitamin D

The evidence suggests vitamin D may matter mainly if you are deficient. In a one-year trial in 54 overweight men who were vitamin D deficient (daily dose of 3,332 IU), total testosterone rose from 10.7 to 13.4 nmol/L in the supplemented group and did not change in the placebo group.^[10] In a 12-week trial in 98 healthy men (average age 39) with normal testosterone and vitamin D levels below 75 nmol/L, supplementation had no effect on total testosterone.^[11] If you suspect low vitamin D, ask your doctor to test your level before supplementing; more is not better, and high doses carry their own risks. See our vitamin D and testosterone article.

Prostate Health: What Every Man Over 40 Should Know

Any discussion of testosterone after 40 should address the prostate, because concerns about testosterone and prostate cancer have shaped medical practice for decades. What the current evidence supports:

• The old idea that more testosterone fuels prostate cancer is now considered too simple.A review proposed a “saturation model”: prostate growth is highly sensitive to androgens at very low levels but becomes insensitive once androgen receptors are maximally bound, which would explain why testosterone treatment in men who are not castrated has little further effect.^[12] It is a conceptual framework, not a guarantee for any individual man.
• Trial data are reassuring but limited. In a randomized trial of 5,204 hypogonadal men aged 45 to 80 who had been screened to exclude those at high risk of prostate cancer, high-grade prostate cancer occurred in 0.19 percent of men on testosterone gel and 0.12 percent on placebo (not a statistically significant difference), but PSA rose more in the treated men.^[13] The average treatment duration was under two years, so long-term risk is not settled.
• Benign prostate enlargement (BPH) is common with age. Weak stream, frequent urination or getting up at night are reasons to see a doctor, and they matter before any testosterone treatment.
• Screening is a conversation with your doctor. Ask when to start PSA testing and prostate exams, especially if prostate cancer runs in your family.

For more detail, read our article on testosterone and prostate health.

Testosterone Therapy: A Medical Decision

Testosterone replacement therapy (TRT) is a prescription treatment for men with diagnosed hypogonadism. It is not a wellness shortcut, and this article cannot tell you whether it is right for you. Here is what the guidelines and major trials say:

The Endocrine Society guideline recommends diagnosing hypogonadism only in men with symptoms and signs plus unequivocally and consistently low fasting morning total testosterone, with the diagnosis confirmed by repeat measurement. It advises evaluating the cause, recommends against starting therapy in men planning fertility in the near term or with conditions such as prostate or breast cancer, elevated hematocrit or untreated severe sleep apnea, and recommends monitoring symptoms, testosterone, hematocrit and prostate cancer risk during the first year of treatment.^[4] In the TRAVERSE trial, men aged 45 to 80 with existing or high risk of cardiovascular disease, symptoms, and two fasting testosterone levels below 300 ng/dL were randomized to gel or placebo. Major adverse cardiac events were 7.0 percent with testosterone versus 7.3 percent with placebo (noninferior), but atrial fibrillation, acute kidney injury and pulmonary embolism were more common with testosterone.^[5] The 300 ng/dL cutoff is the one used in that trial and is widely cited, but laboratories and guidelines differ, and a diagnosis rests on symptoms plus repeated tests, not a single number.

If you want to understand lifestyle options before talking to a doctor, see our guide on testosterone optimization without TRT.

A Note on Supplements

Supplements should never replace the basics or a medical evaluation. The trial evidence for most “testosterone boosters” is limited, short and often industry-funded, and some products have safety concerns. Vitamin D is the clearest case: it may help if you are deficient and appears not to help if you are not (see above). Herbs such as ashwagandha have small trials with mixed results and rare reports of liver injury, so discuss any supplement with your doctor or pharmacist, especially if you take medications or have a liver, thyroid or heart condition. Our supplement guide goes through the evidence one by one.

The Mindset Shift: Train Smarter, Not Harder

The approach that worked in your 20s, long sessions, little recovery, irregular sleep, tends to work less well at 40 and beyond. Many men do better shifting from volume to consistency: sessions you can recover from, enough protein, steady sleep and proactive stress management. Small habits repeated for years matter more than any single intervention.

Key Takeaways

• Testosterone declines gradually with age, around 1.6 percent per year for total testosterone in one large cohort, but individual trajectories vary widely.^[1]
• Body weight is the best-documented modifiable factor, and the association with weight loss appears reversible.^[2][3]
• Sleep, resistance training, protein and stress management support healthy aging whether or not they move your testosterone.
• Prostate-related safety data are reassuring but short-term; discuss screening and any urinary symptoms with your doctor. For men continuing into their 60s, see our guide on testosterone optimization after 60.
• TRT is a medical treatment for diagnosed deficiency with real trade-offs and requires proper medical oversight.^[4][5]

How Thrive Helps

Thrive is a wellness app built for men who want to build healthier daily habits. Track exercise, sleep, nutrition and stress-management habits, see your consistency over time, and bring a clear picture of your routines to your next doctor visit. Thrive is not a medical device and does not diagnose or treat any condition. Try Thrive free on the App Store.