The environment may be a much bigger driver of human health than genetics, which raises questions about the value of genomic sequencing and the push toward personalized medicine, says a team of Stanford scientists studying the immune system.

“Everything starts to look like genetics. And yet, it isn’t, really,” said Mark Davis, lead author of the study and director of Stanford’s Institute for Immunity, Transplantation and Infection. “The big message is the environment matters a lot.”

While Davis’ study was specific to the immune system, it’s likely, he said, that the same environmental influence applies to other body systems and overall health. And while there’s no doubt that genetics plays a huge role in certain diseases and health outcomes, the importance of DNA may be overstated.

Genomic sequencing, which involves reading the genetic makeup of an organism, has become widespread. Scientists are hunting for genetic clues to hundreds of human diseases, from Alzheimer’s and cancer to the flu, and increasingly researchers are promoting the idea of personalized medicine, or targeting treatment to a patient’s DNA. That’s all valuable work, Davis said. But he’s wary of overselling the potential of genomic sleuthing.

His team recruited 78 identical and 27 fraternal twins between ages 8 and 82. They donated blood and other samples, which were tested for 204 different immune system markers, including, for example, the number and variety of certain cells each person has.

Based on the study results, nearly 60 percent of the immune markers were almost totally defined by nongenetic factors — in other words, the environment. And some of the markers became increasingly defined by nongenetic factors with age. Their study was published in the journal Cell.