Sunshine may be related to seasonal patterns of STEMIs

The work included 2,270 STEMI cases throughout both hemispheres and at different latitudes in Italy, China, Scotland, Finland, Japan, Australia, and Singapore.

The researchers concluded that the “summer shift” of STEMI to the nocturnal interval is consistent across different populations, and the sunshine duration (a measure related to cloudiness and solar irradiance) underpins this season‐dependent circadian perturbation. Vitamin D, which in our results seems correlated with this summer shift, is also primarily regulated by the sunshine duration, and future studies should investigate their joint role in the mechanisms of STEMIetiogenesis.

"No study before this has investigated this shift from day hours to nocturnal hours," said Carlo Vittorio Cannistraci, the study's lead author and a theoretical engineer in the Biotechnology Center and the Department of Physics at the Technical University of Dresden in Germany. The shift also is tied to the duration of sunshine in areas around the world closest to the equator that doesn't experience traditional seasons, he said.

The researchers said they noticed the patterns in STEMI occurrence while they were collaborating on another study, published in the AHA's journal Circulation Research in 2013. In that work, they saw a late afternoon peak in their data from Italy and began asking questions about peaks in other countries.

The turning point came when they analyzed cases in Singapore, said Cannistraci, who leads a biomedical cybernetics group at TU-Dresden. In that country, where there is virtually no summer or seasons or wide variations in temperature, they were able to associate the STEMI peaks with sunshine.

"By this study, we really are studying the dark side of the moon – what we don't really know," said the study's co-author, Dr. Enrico Ammirati, a cardiologist at Niguarda Hospital's De Gasperis Cardio Center in Milan, Italy. "We tried to look at the problem of acute myocardial infarction, to look at an area that previous studies didn't examine, how something related to natural phenomena can affect us."

Dr. Patrick O'Gara, a cardiologist who helped write AHA guidelines that doctors use to treat STEMI patients, said the new research highlights gaps in the current knowledge about "the complex interplay" between daily biological cycles and heart attack triggers.

It's important to establish a "mechanistic link between circadian rhythms, sunshine duration, activity patterns, restful sleep" and the stability of the fatty deposits called plaque that can clog arteries, said O'Gara, a Harvard University medical professor and director of strategic planning for the Cardiovascular Division at Brigham and Women's Hospital in Boston.

"The 'summer shift' noted in this analysis may provide clues to a more informed understanding of these processes," O'Gara said.

The study's researchers say their work needs more confirmation, and that they hope they have opened the door to encourage other scientists to study the molecular mechanisms that could link sunshine to these STEMI patterns.

A key part of understanding the results, Cannistraci and Ammirati said, is their analysis is tied not to the amount of light given off by the sun, but by the radiation. So, it can be affected by cloud cover and pollution.

According to authors, the study establishes the notion that the relationship between humans, the environment, and climate is delicate and therefore one should respect the environment because its disturbance can have a negative feedback on our health in unexpected ways.