Men who do little exercise and spend much of their spare time watching TV have lower sperm counts than more active men, a study suggests.
Clocking up 20 hours a week of TV time appears to be detrimental, the US authors from Harvard say in the British Journal of Sports Medicine.
Yet 15 hours or more of exercise a week boosts semen quality, according to the results in nearly 200 college students.
The researchers said more studies were needed to explore the possible causes.
And some experts say men wanting to conceive need to be selective about the sport they do as some types may harm sperm.
Too much time riding a bike or doing long-distance running in tight clothing may not be good, other studies suggest.
Up to a fifth of young men find themselves with a low sperm count, defined as fewer than 20 million sperm per millilitre of semen.
A low sperm count or poor sperm quality is the cause of infertility in about 20% of couples with fertility problems in the UK, and a contributory factor in a further 25% of couples.
This page offers advice for people who think that they, or their partner, may have a low sperm count, known medically as oligozoospermia. It explains the causes of a low sperm count, how you get this problem properly diagnosed, and the treatment options available.
If you have not managed to conceive after one year of trying for a baby, you should see your GP. They will be able to carry out fertility investigations including a semen test to check the quality and quantity of your (or your partner’s) sperm.
About 1 in 10 men will have an abnormal result on the first semen test but this does not always mean they have a ‘true’ abnormality. So, if the results of the first semen test are abnormal, the test should be repeated.
Ideally, this repeat test should be done three months after the first, but if it looks as though your sperm count is very low or you have no sperm at all, it should be repeated as soon as possible.
Similarly, wearing tight underwear rather than boxer shorts has been linked with lower sperm levels.
In the latest study, the researchers from the Harvard School of Public Health asked 189 young men who were students at a university in New York to record how many hours they had been spending doing physical activity and watching TV in a typical week.
The production of sperm is a complex process and requires normal functioning of the testicles (testes) as well as the hypothalamus and pituitary glands — organs in your brain that produce hormones that trigger sperm production. Once sperm are produced in the testicles, delicate tubes transport them until they mix with semen and are ejaculated out of the penis. Problems with any of these systems can affect sperm production. Also, there are problems of abnormal sperm shape (morphology) or movement (motility). Often the cause of low sperm count isn’t ever identified.
Low sperm count Medical causes
Low sperm count can be caused by a number of health issues and medical treatments. Some of these include:
Varicocele. A varicocele (VAR-ih-koe-seel) is a swelling of the veins that drain the testicle. It’s a common cause of male infertility. This may prevent normal cooling of the testicle, leading to reduced sperm count and fewer moving sperm.
Infection. Some infections can interfere with sperm production and sperm health or can cause scarring that blocks the passage of sperm. These include some sexually transmitted infections, including chlamydia and gonorrhea; inflammation of the prostate (prostatitis); inflamed testicles due to mumps (mumps orchitis); and other infections of the urinary tract or reproductive organs.
Ejaculation problems. Retrograde ejaculation occurs when semen enters the bladder during orgasm instead of emerging out of the tip of the penis. Various health conditions can cause retrograde ejaculation, including diabetes, spinal injuries, and surgery of the bladder, prostate or urethra. Certain medications also may result in retrograde ejaculation, such as blood pressure medications known as alpha blockers. Some men with spinal cord injuries or certain diseases can’t ejaculate semen at all, though they still can produce sperm.
Antibodies that attack sperm. Anti-sperm antibodies are immune system cells that mistakenly identify sperm as harmful invaders and attempt to destroy them. This is especially common in men who’ve had a vasectomy.
Tumors. Cancers and nonmalignant tumors can affect the male reproductive organs directly, or can affect the glands that release hormones related to reproduction (such as the pituitary gland). Surgery, radiation or chemotherapy to treat tumors can also affect male fertility.
Undescended testicles. During fetal development one or both testicles sometimes fail to descend from the abdomen into the sac that normally contains the testicles (scrotum). Decreased fertility is more likely in men with this condition.
Hormone imbalances. The hypothalamus, pituitary and testicles produce hormones that are necessary to create sperm. Alterations in these hormones, as well as from other systems such as the thyroid and adrenal, may impair sperm production.
Sperm duct defects. The tubes that carry sperm can be damaged by illness or injury. Some men are born with a blockage in the part of the testicle that stores sperm (epididymis) or a blockage of one of the tubes that carry sperm out of the testicles (vas deferens). Men with cystic fibrosis and some other inherited conditions may be born without sperm ducts altogether.
Chromosome defects. Inherited disorders such as Klinefelter’s syndrome — in which a male is born with two X chromosomes and one Y chromosome instead of one X and one Y — cause abnormal development of the male reproductive organs. Other genetic syndromes associated with infertility include cystic fibrosis, Kallmann’s syndrome, Young’s syndrome, and Kartagener syndrome.
Celiac disease. A digestive disorder caused by sensitivity to gluten, celiac disease can cause male infertility. Fertility may improve after adopting a gluten-free diet.
Certain medications. Testosterone replacement therapy, long-term anabolic steroid use, cancer medications (chemotherapy), certain antifungal medications, some ulcer medications and some other medications can impair sperm production and decrease male fertility.
The volunteers, all aged between 18 and 22, were also asked to provide a sperm sample for lab analysis.
When the researchers compared the survey findings with the sperm test results they found the link between sedentary lifestyle and low sperm count.
Men who were the most physically active, doing 15 hours or more of moderate to vigorous exercise each week by playing football, baseball or basketball for example, had sperm counts which were 73% higher than those who were least physically active.
Those who spent lots of time watching TV or DVDs - at least 20 hours a week - had a sperm count that was 44% lower than men who spent little time in front of the box.
None of the men had sperm counts so low that doctors would classify them as sub-fertile.