Research Links Month of Birth to Disease

ByABC News
October 14, 2004, 1:13 PM

Feb. 3, 2004 — -- You may dismiss astrology as a harmless pseudo-science, but your birthday could have more importance than you think. Some scientists now believe the month in which you were born may predispose you to certain illnesses.

Medical experts worldwide have found specific illnesses and behavioral disorders are more prevalent among people born during certain months or seasons of the year. The list includes asthma, epilepsy, multiple sclerosis, leukemia, dyslexia, diabetes and others.

Schizophrenia, for example, has been shown to be more common among people born in January, February and March. Narcolepsy, a sleep disorder, is more frequent among people born in March and less common among those born in September.

But don't worry that this means you're destined to come down with a particular disorder. Experts agree their findings can't predict what will happen to individuals. They also agree more study is needed to understand the ways your birth month or season influences your health.

So what causes the link between disease and birth month or season? Most scientists suspect environmental factors are the culprit.

For instance, fetal exposure to seasonal viruses like the flu virus, or to a symptom of viral exposure like fever, might be a possible cause.

"Some infectious diseases have a seasonal variation," says Dr. Marvin J. Bittner, epidemiologist with the Veterans Affairs Medical Center in Omaha, Neb. "The reason for these variations is not entirely understood. In other cases, seasonal variation leads to insights. For example, mosquito-borne diseases vary with mosquito populations and factors such as weather."

Researchers also believe neurological and behavioral disorders like schizophrenia might be linked to viral exposure during the second trimester of pregnancy, when fetal neurodevelopment begins.

Other factors occurring during pregnancy have been considered, including seasonal dietary deficiencies, prenatal or newborn exposure to seasonal allergens like pollen, and vitamin D deficiencies over the dark months of winter (vitamin D is synthesized by your body during exposure to sunlight).

No study, however, has been able to prove a definite cause-and-effect relationship.

"Environmental factors are very difficult to study and are very speculative," says Dr. Emmanuel Mignot, professor of psychiatry at Stanford University, whose research discovered the increase in narcolepsy among people born in March. "It's nearly impossible to find out what could be involved, like finding a needle in a haystack."