How your birth month affects your health

People who believe in astrology are convinced that constellations and other heavenly objects prominent in their birth month guide their fates.

Those systems are hardly scientific, but scientists continue to find evidence that the month, or season, that babies are born, or conceived, may have a significant effect on their lifetime health.

Links have been made for illnesses and conditions ranging from nearsightedness and multiple sclerosis to asthma and birth defects.

Yet even when the timing is clear, researchers say it's often difficult to say what's going on in a particular part of the year that influences health often many years later. Of course, there are always theories. For MS, the suspect is low levels of vitamin D in moms peaking around the month of May; nearsightedness seems more likely to affect babies born in spring and summer, and thus exposed to more sunlight at an early age.

One of the more recent connections was made by researchers at Vanderbilt University. They reported last year that children born in early fall - about four months before the height of cold and flu season - have a 30 percent greater risk of developing childhood asthma than those born at any other time of year.

Researchers analyzed birth and medical records for more than 95,000 Tennessee children.

The researchers suspect that fall babies are more susceptible both because they run into the worst of virus season early in their lives, but that some portion of them also has a genetic trait that makes inflammation of the smallest air passage of the lungs - and asthma - more likely.

Experts say 70 percent of babies get a viral infection in the first year of life. But it might be possible for parents in families where asthma is common to either try to time births toward spring, or take extra steps like vaccines or anti-viral medicines to protect babies born in the fall.

Another study, led by a neonatologist at the Indiana University School of Medicine and published in April, found that babies conceived from April through July have higher rates of birth defects.

Dr. Paul Winchester says those months also happen to match the time of year when the highest concentrations of pesticides are found in surface water around the country, according to data from the U.S. Geological Survey and the Environmental Protection Agency.

Winchester and colleagues studied records for more than 30 million births that occurred in the United States between 1996 and 2002. The researchers found the elevated risk for women conceiving in late spring and early summer even among those who did not have other well-established risk factors for birth defects - smoking, alcohol consumption, diabetes or advanced age.

"While our study didn't prove a cause-and-effect link, the fact that birth defects and pesticides in surface water peak during the same four months makes us suspect the two are related," Winchester said.

Even more tentative, but still intriguing, is a possible connection between rainy (and snowy) seasons and autism identified in a study by researchers at Cornell University. The found a connection between autism incidence and precipitation levels among young children in California, Oregon and Washington state born between 1987 and 1999.

Although they suspect, like the birth-defect researchers, that increased runoff or deposition of chemicals from precipitation might be responsible, the Cornell team acknowledged there's no direct evidence of such an environmental trigger.

And, they note, rainy days also tend to keep children indoors, where they could be exposed to more household chemicals, get less sunshine (and vitamin D) or spend more time in front of video screens - all potential suspects for bringing on the disorders in children who might already be genetically susceptible.