Around the age of 30 it is not uncommon for both men and women to experience a strong physical and emotional desire to have a child.
Most couples have no trouble conceiving, but in many countries infertility is on the increase.
Couples struggling to conceive may be pleased to know that, according to a recent finding, certain genes linked to heart disease may also improve your chances of having children.
Australian researchers said the findings seem to offer a potential explanation for why evolution has allowed these genes to persist for centuries.
While lifestyle is clearly important in heart disease risk, scientists have found many genes also influence those odds.
Heart disease in ancient times
"Genes play a very important role in coronary artery disease risk across an individual's lifetime," said study author Sean Byars, a research fellow at the University of Melbourne. In fact, it's estimated that genes account for about 50% of the risk.
Heart disease is a major killer worldwide, and it has long plagued humanity. Scientists have found evidence of clogged arteries in Egyptian mummies, Byars and his colleagues pointed out.
The researchers said that raises a fundamental question: Why haven't the genes that promote heart disease been weeded out by natural selection?
Natural selection is the process by which organisms – including humans – evolve to have better survival odds.
Heart disease and fertility
The new study suggests one answer: Byars' team found that a few dozen genes tied to heart disease might also contribute to people's "reproductive success".
Since heart disease usually strikes later in life, after people have had their kids, it would be a reasonable trade-off for better fertility – at least in terms of survival of the species.
The findings, published online in the journal PLOS Genetics, do not have any immediate implications for managing heart disease or fertility, Byars said.
Heart disease is, of course, a complex condition that involves many different factors. Even if Mother Nature insists that humans carry heart-disease genes, there is still plenty that people can do about it, according to Dr Robert Rosenson.
Rosenson, a cardiologist at Mount Sinai Health System in New York City, pointed to the example of familial hypercholesterolemia (FH).
FH is an inherited disorder caused by a single genetic defect, and it leads to very high "bad" cholesterol levels and a substantial risk of premature heart disease.
But even with those genetic cards stacked against them, Rosenson said, people with FH can prevent or delay heart complications – by taking cholesterol medication, exercising regularly, not smoking and eating a healthy diet.
Hope for the future
"Even if you have a disease-causing genetic trait, lifestyle absolutely makes a difference," Rosenson said.
Genes, he explained, may help explain why one person responds well to a cholesterol-lowering statin, while someone else "gains weight and develops diabetes", for example.
"Someone might develop a drug side effect simply because they've inherited a trait that interferes with a drug-elimination pathway," Rosenson said.
The hope for the future, he said, is to use genetic information to help predict which treatments will likely benefit an individual patient.
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