Why this matters after 40. Testosterone drops slowly with age, and for some men it drops low enough to matter. Signs: low sex drive, weaker erections, low energy, losing muscle or adding belly fat even while training, low mood, poor sleep. Lots of other things cause these too, which is why you test instead of guessing.

The test. Ask your doctor for a total testosterone blood test, or use an at-home kit (tap Get test kit). Most kits have a doctor or nurse review your results. Get blood drawn in the morning (about 7 to 10 AM), when levels are highest. The American Urological Association calls under 300 ng/dL low, and wants a second morning test to confirm it. If it comes back low, your doctor will usually check free testosterone and a few related hormones to find out why.

If it's truly low. Treatment (TRT) is a prescription, not a supplement. It works, but it needs a doctor watching your blood counts and prostate numbers, and it shuts down your own production and lowers fertility. If you might want more kids, say so up front.

What you control, starting today. Sleep 7 to 9 hours (in one study, a week of 5-hour nights cut young men's testosterone by 10 to 15%). Lose waist fat. Lift hard (this plan). Cut back on drinking. Don't crash diet. These move the number more than any pill.

About store "test boosters." Most herbal blends (tribulus, fenugreek, D-aspartic acid and the like) haven't been shown to raise testosterone in men with normal levels. What does help: fixing a real shortfall in vitamin D or zinc, and possibly ashwagandha (below). Tongkat ali has a couple of small studies, not enough yet, and quality varies a lot. Avoid anything sold as "anabolic" or "steroid-like." The FDA has found hidden steroids in some of these products.