What should a man avoid if he wants to have children?

Free radicals are dangerous oxygen molecules said to have a hand in everything from ageing to diabetes and cancer. Sperm actually need low levels of free radicals in order to function (and this is why free radicals are generated naturally as the sperm make their way to the fallopian tubes).

But higher levels will damage the sperm cells, Zita West, a fertility expert, midwife and author of 'Eat Yourself Pregnant' says.

In order to give the sperm the best possible chances of being strong enough and having enough energy to make their journey into the fallopian tube - and of fertilising an egg successfully when they get there - avoiding excess oxidative stress as much as possible is essential.

Causes of free-radical damage in men are:

• Heat: Jacuzzis, tight underwear, heated car seats, mobile phones in pockets and laptops on laps all raise the temperature of the testes, which hang outside the body for the very reason that sperm are damaged by heat!

• Charred barbecued foods

• Trans fats (such as those found in processed foods, deep-fried foods and takeaways)

• Alcohol, nicotine (smoking) and other recreational drugs

• Age, but a healthy diet and lifestyle will keep all the body systems younger for longer 

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