Testosterone: What It Does, What Lowers It, the Tests and the Evidence on Boosters

Testosterone is a sex hormone. In men the testicles are its main producers; women make it too, in much smaller amounts. In both sexes it helps control sex drive and supports the growth of muscle and bone. ICMR-NIN sets no intake figure for it, because it is a hormone the body makes and not a nutrient. The number most readers meet is a laboratory range: across four large cohorts, healthy non-obese men aged 19 to 39 ran from 264 to 916 ng/dL. Body fat, sleep and hard dieting move a man within that range more than any capsule. This entry is part of NNWA's handbook of hormones.

What does testosterone do in men and women?

In both sexes it helps control sex drive and helps muscle and bone to grow. In males it is also involved in the deepening of the voice at puberty, the growth of body hair, the production of sperm and the making of new red blood cells. That list, from the United States National Library of Medicine, explains the symptoms linked with a low level in men: low sex drive, erectile difficulty, infertility, loss of muscle, and thinning bones.

Most testosterone in the blood travels bound to proteins, chiefly sex hormone binding globulin (SHBG) and albumin, and only a small share is free. Levels peak in the morning. A research letter in JAMA puts the fall with normal ageing at 1 to 2 per cent a year. The handbook's entry on insulin and insulin resistance covers a hormone that often shifts alongside it.

How do body fat, sleep and dieting change testosterone?

All three move it, and in a predictable direction: excess body fat, short sleep and a large energy deficit each lower it, and correcting them raises it again. A meta-analysis of 24 studies found that weight loss in obese men, by a low-calorie diet or by bariatric surgery, was followed by a rise in total testosterone. Surgery raised it about three times as much as diet, and the degree of weight loss was the best predictor of the rise.

Sleep acts within days. Ten healthy men with a mean age of 24 slept ten hours a night in a laboratory and then five hours a night for a week. Their daytime testosterone averaged 16.5 nmol/L after the short nights against 18.4 nmol/L when rested, a fall of 10 to 15 per cent, and their vigour scores dropped with it. It was a small sample, so the size of the effect is approximate. ICMR-NIN's Dietary Guidelines for Indians advise six to eight hours of sleep a day.

Hard dieting is the factor gym-goers overlook. Soldiers on an eight-week course who ran average energy deficits of 1,000 to 1,200 kcal a day, with heavy work and little sleep, saw testosterone fall close to castrate levels, and it recovered promptly once they were fed. A year-long case study of one drug-free bodybuilder recorded the same curve: down by three quarters during contest preparation, back to baseline afterwards. A moderate deficit set with the calorie calculator is a different thing from months of semi-starvation.

The Indian picture: weight, diabetes and PCOS

India has no national survey of testosterone, so the Indian evidence comes from clinic studies and from surveys of the conditions that travel with it. In a study of 900 Indian men with type 2 diabetes, 20.7 per cent had low testosterone with symptoms. Another 50.1 per cent had the symptoms with a normal level, so the authors warned that symptoms alone cannot make the diagnosis.

Among women the picture is the opposite problem, an excess. An ICMR task force screened 8,993 women aged 18 to 40 across five zones of the country and put the prevalence of polycystic ovary syndrome at 19.6 per cent by the Rotterdam criteria, 13.6 per cent by the Androgen Excess and PCOS Society criteria and 7.2 per cent by the older NIH criteria. Fat around the middle tracks with these shifts in both sexes, so the waist to hip ratio calculator is a sensible home check.

Do zinc and vitamin D raise testosterone?

Only where there was a shortage to correct, on the evidence read here. In a 1996 study, four young men whose dietary zinc was restricted for 20 weeks saw serum testosterone fall from 39.9 to 10.6 nmol/L, and nine older men who were marginally zinc deficient saw it rise from 8.3 to 16.0 nmol/L after six months of supplementation. These tiny groups show what deficiency does, not that extra zinc helps a man who has enough.

ICMR-NIN's 2020 allowance for zinc is 17 mg a day for men and 13 mg for women, an amount that food can supply; the zinc entry and the zinc table for Indian foods list the sources. Vitamin D tells a similar story. In one trial, overweight men who began with deficient vitamin D and testosterone at the low end of the range saw total testosterone rise from 10.7 to 13.4 nmol/L over a year of supplementation. In a later trial of 98 healthy men with normal testosterone, 12 weeks of vitamin D had no effect on it. The vitamin D entry covers Indian requirements.

Do testosterone boosters and ashwagandha work?

Mostly the claims run ahead of the data. Researchers who examined 50 products sold as testosterone boosters found that 90 per cent claimed to raise the hormone, yet only 24.8 per cent had any published data showing an increase. For 61.5 per cent there were no data at all, and 10.1 per cent contained an ingredient with data suggesting a decrease. Thirteen products exceeded an upper intake limit for zinc, niacin or magnesium.

Ashwagandha has more behind it than most, with limits. A systematic review of 32 trials of single herbs found positive effects for ashwagandha and fenugreek extracts, but only 9 of the 32 trials showed a significant rise and only 6 were at low risk of bias. In an Indian trial of 57 young men starting resistance training, testosterone rose by 96.2 ng/dL with the extract against 18.0 ng/dL with placebo over eight weeks. In overweight men aged 40 to 70, salivary testosterone rose 14.7 per cent more than with placebo, with no difference in fatigue, vigour or sexual wellbeing. The ashwagandha entry covers safety.

Which tests does a doctor order, and what do they measure?

The first test is total testosterone, which measures the bound and free hormone together. The Endocrine Society's guideline asks for a fasting morning sample, measured with an accurate assay, and for the test to be repeated before any diagnosis; blood is usually drawn between 7 and 10 in the morning, when levels are highest. The guideline makes a diagnosis of hypogonadism only in men who have both symptoms and levels that are unequivocally and consistently low. What a given number means for you is the doctor's judgement.

Women are a harder measurement problem. The global position statement on testosterone for women says that the direct assays most laboratories use for total and free testosterone are highly unreliable in the female range, and that no blood level separates women with and without sexual difficulties. In men, too, much of the difference between cohorts came from the assays, so each report should be read against the range printed on it.

A worked example: reading one afternoon report

This is an illustrative case, not a real person, and the figures are chosen to show the reasoning, not to say what is normal for anyone. A 31-year-old man in Pune has dieted for 16 weeks for a physique contest, sleeps about five hours a night, and orders his own test at 4 pm after reading about boosters. The report says total testosterone 310 ng/dL.

Anabolic steroids: the risks to the heart, hormones and mind

Anabolic-androgenic steroids are testosterone and its synthetic relatives taken in amounts far above what the body makes. The Endocrine Society's scientific statement links their use to an increased risk of death and to cardiovascular, psychiatric, metabolic, endocrine, liver, kidney and musculoskeletal disorders. In a study of 140 experienced male weightlifters, the 86 long-term users had weaker heart pumping function than non-users, with a left ventricular ejection fraction of 52 against 63 per cent, and more plaque in their coronary arteries.

The hormonal cost is the one users least expect. Outside steroids shut down the body's own production, and the statement notes that after a long course this suppression can last months or years, with some men never regaining normal levels. It lists infertility, breast enlargement in men, testicular shrinkage, acne, mood disorders, liver damage with oral forms and tendon rupture among the effects, and estimates that about 30 per cent of users become dependent. FSSAI's regulations state that no hormones or steroids may be added to any health supplement or nutraceutical.

High testosterone in women: the PCOS link

When a woman is tested, it is usually for signs of too much testosterone, not too little. The National Library of Medicine lists those signs as excess hair on the face or body, thinning hair on the scalp, acne, voice changes, irregular or absent periods and difficulty conceiving, and names polycystic ovary syndrome among the causes. Raised androgens, in the blood or as visible signs, are one of the features on which PCOS is diagnosed; 257 women in the Indian survey had this feature alone.

Among the 1,224 Indian women with PCOS in that survey, 43.2 per cent had obesity and 24.9 per cent had metabolic syndrome, so the condition is metabolic as well as reproductive. The 2023 international guideline keeps its emphasis on a healthy lifestyle, on evidence it rates as low to moderate in quality. NNWA's guide to the PCOS diet in India covers the food side. Diagnosis and medicines belong to a gynaecologist or endocrinologist.

Common myths and mistakes

Three mistakes recur. The first is testing at the wrong time: an afternoon sample, or one taken after a week of poor sleep, can sit well below a morning value. The second is treating one low reading as a diagnosis, when the guideline asks for a repeat and for symptoms. The third is reaching for a product when the level is responding to a long energy deficit and will follow food and sleep back up.

When should you see a doctor about testosterone?

See a doctor, not a trainer or a supplement shop, when symptoms persist: in men, low sex drive, erectile difficulty, infertility, breast enlargement or loss of body hair; in women, new facial hair, scalp hair loss, a deepening voice or irregular periods. Testosterone is a prescription medicine. Under the Endocrine Society's guideline it is for men with symptoms and consistently low levels, after the cause has been looked for, and it is not started in men planning a pregnancy with their partner in the near term. Nothing on this page is advice about doses.

Learning this with NNWA

Hormones and the habits that shift them are taught at NNWA, a private skill academy in Kolkata that runs its classes online in English and Hindi. Courses such as Sports Nutrition and Women's Health and PCOS train people to coach healthy clients on food, training and sleep and to refer hormonal and medical questions to a doctor. None of them is a degree or a dietitian qualification.