Kickboxing can cause damage to the pituitary gland, a pea-sized gland found at the base of the brain just behind the bridge of the nose, scientists say.
The gland produces a range of hormones that control, among other things, the body's regulation of metabolism coping with daily stress, general well being and sex drive.
The team at Erciyes University Medical School in Turkey measured the levels of these hormones in 22 amateur kickboxers (16 men and six women) and compared these to healthy people of the same age and sex, according to BBC News.
They found that found that six of the kickboxers were deficient in at least one hormone compared with the healthy group. The researchers say the head is one of the most common sites of injury for both amateur and professional kickboxers.
This is the first time that amateur kickboxing, which uses kicks and punches, has been shown to cause damage to the pituitary resulting in insufficient hormone production, said Professor Fahrettin Kelestimur, who led the research.
Although more research was needed to understand how the pituitary gland is damaged and to develop more effective head protection gear for kickboxers, the researchers say amateurs with head injuries should be screened.
People who take part in combative sports and are exposed to repeated head trauma should be screened to ensure their pituitary is working properly, the researchers recommend.
Around a million people around the world take part in kickboxing. Kickboxers, however, say they are unaware of such injuries.
A spokesperson for the World Kickboxing Association said: "I have never heard of any such damage." He added that amateurs, though not professionals, already wore head protection.