Causes of low testosterone levels: testicular injuries or infections, chemotherapy or radiation treatments for cancer, pituitary gland disease or other hormonal disorders, medications such as corticosteroids and opiates to relieve pain, genetic conditions such as Klinefelter syndrome, alcohol and drug abuse. There have been hundreds of studies showing that certain foods have detrimental effects on testosterone.
For men who are prescribed testosterone replacement therapy, it usually takes three to six months to take effect, Farooq says. Some men may see improvement sooner, but for most men it's a gradual process, Farooq says.
Testosterone levels change throughout the day in men, peak around 4 to 8 in the morning and fall to their lowest level approximately 12 hours later. They can also vary throughout the year, although these seasonal highs and lows will differ around the world.