Research library
Plain-language summaries of the studies behind the guides, each with an honest read on how strong the evidence is.
How we rate the evidence
Strong
Replicated, controlled evidence that points the same way.
Moderate
Randomized evidence exists, but effects are small or study quality is limited.
Limited
Results are null, inconsistent, or the evidence is thin.
| Topic | What the research says | Evidence |
|---|---|---|
| How low testosterone is actually diagnosed | Diagnosis needs a low blood level on two early-morning tests, plus symptoms. | Clinical guideline |
| Sleep and testosterone | A week of 5-hour nights lowered daytime testosterone by 10 to 15 percent. | Strong |
| Weight loss and testosterone | Losing excess weight is linked to higher testosterone in men with obesity. | Strong |
| Exercise and resting testosterone | In trials, training barely moved resting testosterone in men with normal levels. | Limited |
| Vitamin D and testosterone | Reviews of randomized trials disagree. Evidence for a boost is weak. | Limited |
| Ashwagandha, fenugreek, and other herbs | Ashwagandha and fenugreek show small average increases in trials of limited quality. | Moderate |
These summaries are for general education and are not medical advice. Ratings are our reading of the published research and can change as new studies appear. Each article lists its sources and the date it was last updated.
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