A study by British researchers seems to upend some standard medical advice for men: They found that smoking, heavy drinking, doing drugs, and being overweight doesn't affect sperm, reports the BBC. Researchers compared samples in about 2,000 men and found "little evidence" that lifestyle has any impact on semen quality. This being a medical study, however, the doctors took pains to note that they still don't think smoking, excessive drinking, doing drugs, and overeating are wise choices—it's just that they won't affect the ability to have kids.
"Delaying fertility treatment then for these couples so that they can make changes to their lifestyles, for which there is little evidence of effectiveness, is unlikely to improve their chances of a conception and, indeed, might be prejudicial for couples with little time left to lose," says one of the researchers. One piece of advice that holds: Go with boxers over tighty whities to boost sperm count.