Much has been written about the ticktock of women’s biological clocks and the inherent risks when older women get pregnant.

Now, older fathers may need to be aware of what their age could mean to offspring. Risk of non-Hodgkin’s lymphoma is higher for children of older men, according to City of Hope researchers — a finding that adds to a growing body of evidence suggesting that men, too, may have a biological clock.

The study is one of the first to examine the relationship between parents’ age and their adult offspring’s likelihood of facing cancers of the blood and immune system. Yani Lu, Ph.D., a postdoctoral fellow in the Division of Cancer Etiology, led the study, which was released in the American Journal of Epidemiology on June 15.

“As a man, you may think, ‘I can have a baby at 50 or 60 and live long enough to see him go through college.’ But there may be other risks for your child down the line, and you may want to be conscious of those risks,” said Lu.

Lu’s research drew upon data from the California Teachers Study. Initiated in 1995, this project tracks the health, lifestyle choices and demographic information of nearly 133,500 female teachers and administrators in the California public schools’ retirement system. The teachers study is led by Leslie Bernstein, Ph.D., director of the Division of Cancer Etiology in the Department of Population Sciences and Lu’s mentor.

In the latest project, researchers focused on 110,999 women, 819 of whom had been diagnosed with a hematological malignancy. The study revealed that participants born to fathers older than age 40 faced a 59 percent greater risk of non-Hodgkin’s lymphoma compared to similar women born to fathers younger than 25.

“For adult-onset malignancies, people seldom think back” to factors early in life, Lu said. “Diagnosis for nonHodgkin’s lymphoma occurs closer to the age of 70, so why would in utero factors be related to risk?”

In the study, the fathers’ age had no effect on risk for acute myeloid leukemia or multiple myeloma. Maternal age did not significantly influence risk for blood cancers.

Science has shown that the ticking biological clock is associated with a higher incidence of health issues in children of older mothers. These women face greater risk of miscarriage and increased risks of bearing children with low birth weight or serious health issues such as Down’s syndrome. A recent, large study suggested that children of women over 40 have a greater chance of having autism.

Similar findings among older fathers are scanty, although research going back almost 100 years suggests that these men are more likely to produce children with certain rare birth defects. Numerous studies also show that offspring of older men have a greater risk of developing schizophrenia.

As Lu noted, however, a burgeoning field of research suggests a father’s age at conception may play a more significant role in his progeny’s health than once thought. Recent investigations indicate that children of older fathers have a greater chance of prostate and breast cancers in adulthood as well as some blood cancers during childhood.

Lu believes the male biological clock might relate to mutations that can accumulate in a man’s reproductive cells over the course of a lifetime. Such cells divide more rapidly than a woman’s reproductive cells. More divisions lead to more chances for abnormalities to arise.

Older parental age also appears to be associated with longer length of offspring’s telomeres, the end caps on chromosomes, which might be linked to non-Hodgkin’s lymphoma risk, Lu suggested.

Because non-Hodgkin’s lymphoma is actually a cluster of related diseases with about 30 subtypes, Lu plans to examine how paternal age and other health factors during the early years of life influence risk for specific disease subtypes.

Sophia S. Wang, Ph.D., associate professor of population sciences, was the paper’s senior author. The National Institutes of Health and the California Breast Cancer Research Fund funded the research.