By Katherine Unger Baillie

Forget birthstones and astrological signs; the month in which you were born may carry serious significance for your health.

A research project involving a team from Penn’s Perelman School of Medicine and School of Veterinary Medicine is teasing out a link between birth month and cardiac disease risk, looking at both humans and dogs. The main thrust: Being born in the summer heightens the risk of disease later in life.

“Dogs are more similar to humans than many other animal models,” says Mary Regina Boland, a biostatistician at Penn Medicine. “They’re pets, so they live in the same environment as we do, but they also can naturally develop cardiovascular disease.”

Boland had been examining the link between birth month and heart disease for a few years, relying on electronic health records, but encountered challenges when accounting for biases and disparities reflected in the data. So she turned to another source.

“I started wondering whether there were any animal models that could potentially support this,” Boland says.

Exploring datasets for pet dogs, Boland realized she needed colleagues in the veterinary world to help her navigate. She connected with two veterinary cardiologists at Penn Vet, Anna Gelzer and Marc Kraus. Together, they analyzed datasets from Penn Vet and the Orthopedic Foundation for Animals, an organization that supports research on inherited diseases in pets.

In a study published earlier this year in Scientific Reports, Boland, Gelzer, Kraus, and colleagues found a strong link between birth month and cardiac disease risk in canines: Those born in the summer months were predisposed to developing heart problems, with the risk soaring up to 74 percent higher than expected for dogs born in July.

In that work, as well as prior studies using human health records, researchers pointed fingers at air pollution as a likely culprit for this connection. It’s believed that exposure to fine air particulates—which are at their highest levels in the summer—somehow leads to harmful physiological changes in utero that may not manifest for decades.

Dogs prove a useful parallel subject to humans for these sorts of studies, the researchers note. “Their life spans are shorter, so if they’re going to develop a condition it will show up in a reasonably compressed timeframe compared to humans,” says Kraus.

That project is still in its early stages, but could have a variety of implications for reducing disease risk.

“For dog breeders, it’s pretty easy to control when puppies are born,” says Gelzer. “With June and July having the highest risk for heart disease, we could just advise to breed during months that wouldn’t result in these birthdays.”

When it comes to humans, dictating which month a baby will come into the world is not as straightforward, but insights gleaned from research in dogs have the potential to help uncover the molecular mechanisms that lead to birth-month effects.

For now, the Penn researchers are brainstorming ways to explore those mechanisms, such as statistical deep dives, genomic sequencing, or microbiome analyses, to potentially locate new intervention targets. They’ve also recently begun to explore connections between cancer risk and birth month, collaborating with Penn Vet’s Nicola Mason, a clinician and researcher who has applied immunotherapy approaches to treating cancer in dogs.

“This doesn’t mean there shouldn’t be any more summer babies,” Boland says, “but the findings we generate could be an entry into some very interesting questions about the drivers of these connections.”

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