A new study has linked caffeine with miscarriages.
People who drink more than a little caffeine when they're trying for a pregnancy are more likely to lose that pregnancy early on, the study found. And that goes equally for men or women.
When either men or women drank three or more cups a day of caffeinated drinks before pregnancy — sodas, energy drinks or coffee — the woman was nearly twice as likely to lose that pregnancy early on. And if women consumed more caffeine after they conceived, they were also more likely to miscarry.
It's one of the most detailed studies yet to look at something that has been noted for a while now — that high caffeine intake seems to be linked with pregnancy loss.
And it's one of the first to show that what men eat or drink can affect fertility.
"There's something about drinking caffeinated beverages that is associated with pregnancy loss," said Germaine Buck Louis of the National Institute of Child Health and Human Development, who led the study.
But women who took multivitamins before they got pregnant and early in pregnancy were 50 percent less likely to miscarry, the study found.
Their findings come out of an intensive study of 344 couples in Texas and Michigan who have agreed to be watched as they try to conceive. They wrote down every caffeinated drink they had, every serving of fish, every alcoholic drink, were weighed regularly, gave urine, blood, saliva and semen samples and the women took regular pregnancy tests.
The idea: to see what might affect a woman's ability to get pregnant and stay pregnant.
There will be answers later to questions about mercury from fish and chemicals such as pesticides. This study looks at caffeine.
"Our findings provide useful information for couples who are planning a pregnancy and who would like to minimize their risk for early pregnancy loss," Louis said.
Of the 344 pregnancies, 28 percent of them ended in miscarriage: 98 in total, the team reports int he journal Fertility and Sterility.
Women who were over 35 had twice the risk of an early miscarriage as younger women - that's long been known.
But drinking three or more caffeinated beverages a day raised the risk of early pregnancy loss by 74 percent. That held whether it was before conception or afterwards.
"Our findings also indicate that the male partner matters, too," Louis said. "Male preconception consumption of caffeinated beverages was just as strongly associated with pregnancy loss as females'."
The study did not look for differences among various caffeinated drinks, but lumped coffee and tea together with sodas and energy drinks.
Dr. Zev Williams of the Albert Einstein College of Medicine and a spokesman for the American College of Obstetricians and Gynecologists said an important point to note is that a little caffeine is okay.
"So many studies, including this one, show that one to two cups of caffeine is not harmful," Williams said.
"And what I do end up seeing not infrequently, an effort to really be as thorough as possible, a lot of women will go cold turkey on caffeine. And what ends up happening is invariably these women will then develop rebound headaches and take medications to treat the headaches. Those medications may be harmful," added Williams, who was not involved int he study.
"So, it's probably better to just have one to two cups of coffee a day and avoid to having those medications to treat a rebound caffeine withdrawal headache than to go completely cold turkey. "
Louis said there has been a debate about whether caffeine causes miscarriages, or whether women who instinctively stop drinking caffeine early in pregnancy have a healthier pregnancy to start with. Because her study looked at caffeine consumption right before pregnancy, before a woman could develop an aversion to the stuff, it supports the idea that it's the caffeine itself causing the miscarriage, Louis said.
The good news is that taking a multivitamin really helps.
'We were really surprised at how strong the reduction in risk was," Louis said.
"We think this is really good news. We know that vitamins protect against a lot of other adverse pregnancy outcomes."
The Centers for Disease Control and Prevention recommends that women planning to become pregnant take folic acid, a type of B vitamin, and avoid alcohol and tobacco smoke. Not all multivitamins are safe and most doctors recommend a specially formulated prenatal vitamin.
Dr. Rebecca Starck, who chairs the gynecology department at the Cleveland Clinic, said the study cannot show cause and effect.
"The main message of the study is that it's important to seek preconception counseling," said Starck, who was not involved in the research.
"Anybody of childbearing age who is contemplating pregnancy should maintain a healthy diet and healthy lifestyle and someone who is going to conceive should be aware of effects of lifestyle on the offspring."
Starck noted that miscarriage is common and the study confirmed that: 25 percent to 30 percent of pregnancies end in miscarriage.
The study did not ask people what else they ate or drank besides alcohol and caffeinated beverages. Louis says it will be important to ask people about decaffeinated sodas, for instance. She said the study cannot answer questions about whether people who eat healthier diets — with more fruits and vegetables and less salt and fat — are better able to conceive and keep a pregnancy.
As with all medical and scientific studies, each one builds on the other, and it will take larger studies to answer some of the questions.