I've heard that caffeine affects fertility. Does it, and if so, how?

Caffeine may lower your chances of conceiving, even if you don't drink or eat large quantities of the stimulant, but the evidence is not conclusive.

One widely reported study found that taking in more than "moderate amounts" of caffeine can lower your likelihood of conceiving by as much as 27 per cent compared to women with low caffeine intakes (Hatch and Bracken 1993). Moderate amounts, in this case, were the equivalent of two cups of coffee a day or four cups of tea or five cans of cola, which works out at about 200 milligrams (mg). In this study, even modest consumption appeared to hinder conception, with women who drank only one to two cups daily lowering their chances of conceiving by 10 per cent.

However, other studies have reached different conclusions. One study found that drinking half a cup of tea each day doubled the chances of conception per cycle, while other caffeinated drinks had no effect (Caan et al 1998). Another study found that women who had an intake of 400-700mg of caffeine a day had higher rates of conception than women who had low intakes, but women with intakes of over 700mg per day took longer to conceive (Florack et al 1994). The conclusion of another prospective study suggested that caffeine had no effect on conception at intakes of less than 200mg per day (Jensen et al 1998). The evidence is clearly contradictory, so what should you do?

After reviewing all the available evidence in 2001, the Organisation of Teratology Information Services based in the US and Canada concluded that: "Low to moderate caffeine consumption (less than 200mg per day) does not seem to reduce a woman's chance of becoming pregnant."

If you're receiving fertility treatment then reducing your caffeine intake could help. There is clearer evidence that caffeine reduces the chance of success for women trying to have a baby using assisted reproductive technologies, such as IVF or GIFT (Klonoff-Cohen et al cited in NCCWCH 2004: 95).

Researchers don't really know why or how a high caffeine intake could be related to delayed conception or infertility. One theory suggests that the stimulant affects ovulation by causing changes in hormone levels, which in turn hampers conception.

If you've been trying to get pregnant for several months without success, try limiting your total intake of caffeine in coffee, tea, cola and cocoa, especially if you regularly take in more than 200mg a day. As current recommendations are to keep your caffeine intake at these lower levels once you become pregnant, it makes sense to get into the habit while you're trying to conceive.

How much caffeine is in my favourite foods and drinks?

Caffeine is a common ingredient in food and drinks, so getting a big dose is easier than you might think. The following is a quick guide, based on information from the Food Standards Agency, (FSA n.d.) as to how much caffeine there may be in your favourite drinks and chocolate bars:

• 1 mug of instant coffee = 100mg
• 1 cup of instant coffee = 75mg
• 1 cup of brewed coffee = 100mg
• 1 cup of tea = 50mg
• 1 can of cola = 40mg
• 1 can of "energy" drink = 80mg
• 1 x 50g bar of plain chocolate = up to 50mg
• 1 x 50g bar of milk chocolate = up to 25mg

You can see that if you had a couple of mugs of coffee, a can of coke and a chocolate bar in one day you'd already be almost be up to 200mg advised limit.

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