How diseases can be linked to your month of birth

A new study done by researchers from Columbia University have found a significant link between birth month and disease risk, after studying data collected from some 1.7 million New York patients over a 28-year period.

They found that the risk of heart disease is substantially higher for people born in March than other months of the year.

Overall, people born in the US autumn months of October and November had the highest disease risk and were found to be particularly vulnerable to acute bronchitis, viral infections and attention deficit hyperactivity disorder (ADHD).

However, for certain cardiovascular diseases including atherosclerosis, where blockages in arteries can cause a fatal blood clot, spring births in March and April were found to be most susceptible.

May births were found to have the lowest risk of developing disease.

The scientists behind the research have noted that other variables, such as an unhealthy diet and lack of exercise, play a far greater role in susceptibility to disease and advised that prospective parents should not worry about rearranging their reproductive calendars.

The study, published last week in the Journal of American Medical Informatics Association, looked at 1,688 diseases to establish whether there was any link to birth month. The research confirmed the link between birth month and 39 diseases, including asthma and myopia (short-sightedness), which has previously been discussed in medical literature.

However, the study also found new links between 16 diseases, including nine types of heart disease, with the time of the year when someone is born. Some 610,000 people die in the US each year from heart disease, making it the country's leading cause of deaths.

In some cases, the research team were able to offer realistic explanations for the link. For example, the researchers suggest that babies born in spring may suffer from a vitamin D deficiency, which has previously been identified as a risk factor in developing hypertension. Mothers of spring babies would have been pregnant throughout the dark winter months, when reduced sunlight levels mean that their vitamin D levels fall.

However, in other cases, the link remains as yet unexplained. The risk of nonvenomous insect bite, for example, was found to be highest in October and lowest in February, with the researchers offering no suggestions as to why.

Connections between certain diseases and birth month have been observed before. A 1983 Danish study found that people born in the Danish summer, when there is a comparative abundance of home dust mites, were 40% more likely to develop asthma.

Last year, a Swedish team found that children born later in the year were more vulnerable to ADHD, partly due to their relative immaturity when starting school. The age cutoff for Swedish schools is 31 December, the same as schools in New York City, possibly explaining the high degree of correspondence between the results of the Swedish study with the new research.