Sperm health.
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Sperm health.

You two have talked. You're ready. You want to try to have a baby. You've got the first part of that process down pat, but then a zillion different factors determine whether or not she actually gets pregnant. A big one that often gets overlooked? The health of your sperm.

Sperm that swims fast and is shaped how it should be has a greater chance of reaching and fertilizing the egg. And the more semen you've got, the better. But lots of things can lower sperm count and make your swimmers less vital, some of which are completely out of your control. According to a new study from Israel, even the time of year can impact sperm quality.

Researchers evaluated 6,500 semen samples collected from a fertility clinic over three and a half years and found that, overall, sperm was much healthier in the winter and early spring. It then dipped in concentration and motility (how well sperm swims forward) in the summer and fall.

Dr. Paul Turek, an expert in men's reproductive health and founder of the Turek Clinic in San Francisco, isn't surprised by these results. He says humans, like many other mammals, are sensitive to day-night cycles and programmed to reproduce certain times of the year. He also says previous research has shown that guys who work outside in the summer have less healthy sperm, because the heat impairs production.

But this doesn't necessarily mean you've missed your baby-making window this year. Even though warmer weather and longer days can impact sperm health, Turek says other factors – ones you can control – play a larger role, such as drinking too much booze, not managing a disease like diabetes, or carrying too many or too few pounds. "Fat men have lower sperm counts," he says. "Same goes for guys who are too skinny." And that ties right back to diet. Turek says eating a lot of saturated fat can impair sperm count, while lean meats, nuts, and antioxidant-rich fruits and vegetables can boost it. He says stress is another huge sperm saboteur because it messes with your hormones.

"Basically, sperm production is like an engine that wants to run fast," he says. "If you treat it right, it will go as fast as it can. But if you fill the tank with water instead of gas, you'll have a problem. What keeps the rest of your body healthy will also keep you reproductively healthy."