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Women who want to have a baby are well aware of how their lifestyle and daily habits can affect their chances of becoming pregnant and having a healthy baby. There's now a growing body of evidence showing men's behavior before pregnancy may also be important.
A new report linking caffeine consumption to miscarriage, found that 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.
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A dad's preconception behavior can also have long lasting effects on his offspring. In recent years, researchers have discovered evidence that a host of lifestyle factors can impact sperm, including stress, overeating, drug abuse, and heavy drinking.
“We always tell women they need to stop drinking and they shouldn’t smoke when they’re trying to get pregnant,” says Dr. Jesse Mills, an associate professor of urology at the University of California, Los Angeles, and director of the Men’s Clinic at UCLA. “Guys have gotten a free pass all these years."
The good news is that most of the harm to sperm is recoverable, Mills says. Despite bad habits, the effects are reversible with a turnaround in lifestyle.
That's because men are always making new sperm. If a man is planning to become a father, adopting good habits for a few months ahead of time which will allow new, healthy sperm to be produced while the sperm with “brittle” DNA due to bad habits die out.
But it’s not just about pregnancy viability.
Much of the new research suggests that fathers' lifestyle habits can affect children throughout their lives. Molecules related to these habits make their way into the sperm and, in a process called epigenetics, work like a dimmer switch heightening or lessening the effects of genes inherited by the child.
A few factors:
Studies that looked at stressed out dads found “increases in the offspring’s susceptibility to different forms of stress,” says Dr. Eric Nestler, the Nash Family Professor of Neuroscience and Director of the Friedman Brain Institute.at the Icahn School of Medicine at Mount Sinai. Nestler was one of the first scientists to discover the connection.
Men who smoke pot may damage their sperm, according to a 2015 study from the University of Copenhagen. Smoking marijuana more than once a week lowered sperm counts 29 percent, on average, compared to those who didn't smoke or did so less frequently.
A raft of recent studies published found that a father’s eating habits may affect how his offspring metabolize glucose and deal with cholesterol.
One intriguing small study published in Cell Metabolism in February looked at how gastric bypass surgery impacted obese men’s sperm. Researchers found a certain epigenetic signature in the sperm of obese men that changed as the men lost weight. And the changes, the researchers wrote, “were notably at gene regions implicated in the central control of appetite.”
Two mouse studies published in Science in December found that paternal diets altered the metabolism of offspring through small molecules called RNAs. One found that daughters of male mice that consumed a high-fat diet developed impaired glucose tolerance and insulin resistance, which are related diabetes risk. The second study found that fathers on a low-protein diet produced altered cholesterol metabolism in offspring.
These effects aren’t necessarily good or bad, says Dr. Oliver Rando, a coauthor on the cholesterol study and a professor of biochemistry and molecular pharmacology at the University of Massachusetts School of Medicine.
“The problem is when there is a mismatch between the effects of the diet and the environment the offspring are going to grow up in,” he says, adding that if babies inherit a tendency to use food efficiently, for example, then growing up in a world where food is plentiful could be unhealthy.
The caffeine effect seen in the new study might also be due to RNAs passed along through the dad's sperm, says Courtney Lynch, coauthor of the miscarriage study and an associate professor of obstetrics and gynecology & pediatrics at the Ohio State University College of Medicine.
Sometimes the effects are counterintuitive.
Researchers found that male mice who consumed large amounts of alcohol produced sons that shied away from liquor.
“In other words, paternal alcohol exposure seemed to protect male offspring from excessive drinking,” says Gregg Homanics, a professor of anesthesiology and pharmacology & chemical biology at the University of Pittsburgh, who led the study. “It is remarkable that similar results were observed by investigators at the University of Pennsylvania following paternal preconception cocaine exposure."
In the end, the dad-effects are small compared to a child's own DNA and environment, Rando says. “These are not the major drivers of metabolic risk,” he explains. “The major drivers are how you eat and your genome.”