The season in which you are born may affect everything from your eyesight to your eating habits and overall health later in life, according to a blossoming field of research. The latest study shows that spring babies are more likely to suffer from anorexia nervosa as adults.
"We found an excess of anorexia births in the spring months compared to the general population," said study researcher Lahiru Handunnetthi, of the Wellcome Trust Center for Human Genetics. "The idea is that there is some sort of risk factor that varies seasonally with anorexia."
The researchers found that eight out of every 100 people born between March and June had anorexia compared with 7 percent of those without anorexia. This is a 15 percent increase in risk for those born during these spring months.
Previous studies have found similar links between spring births and various disorders, including schizophrenia, multiple sclerosis and even Type 1 diabetes. It's possible these diseases are linked to some environmental influence during gestation or the first few months of life, though researchers aren't sure what that could be.
The leading candidates including vitamin D levels, infections that come and go seasonally, changes in nutrition, and even possibly weather fluctuations, Handunnetthi told LiveScience.
These changing environmental factors seem to influence a wide array of conditions:
- A study from 2003 published in the Journal of Nutrition showed that African-American babies born in the summer and fall were smaller than those born at other times. Also, babies of African-American and Puerto Rican decent gained less weight in their first four months if they were born in the fall.
- Babies born in the fall have a 9.5 percent risk of having food allergies, up from 5 percent for babies born in June and July. Those babies born in November or December were also three times more likely to suffer from eczema and wheezing. That study was published in 2010 in the Journal of Epidemiology and Community Health.
- Moderate and severe nearsightedness, or the inability to see well at long distances, is highest for babies born in the summer months, suggests research published in April 2008 in the journal Ophthalmology.
- Birth month might even affect your biological clock, a mouse study published in 2010 in the journal Nature Neuroscience showed. Mice born in the winter were less able to adapt to a summer light cycle, which could be related to the increased risk of mental health disorders in humans born in the winter, the researchers speculated.
- Leukemia has also been linked to being born in the spring, with a peak in April.
Birth month has even been linked to longevity, which could be because of these other adverse health effects. Studies in Austria and Denmark have found that those born in the fall live longer than people born in the spring.
"When we look at diseases we need to identify the risk factor that led to them," Handunnetthi said. "In general, risk factors could be environmental or genetic. Genetic risk factors you are born with and can't really change. If you identify environmental factors you can mediate them to carry out prevention studies."
These environmental causes are still unclear, though some of these birth-month effects may be related. "Perhaps a risk factor is playing a part that is common to all these conditions but we don't know that yet," Handunnetthi said.