Study: Increased solar activity can decrease lifespan by five years.

Monday, January 12, 2015, 8:58 AM - A good amount of exposure to our sun's life-giving rays is touted as an easy way to improve health and your mood.

But now, a new study from Norwegian researchers says there's a dark side: Periods of heightened solar activity may shave years off the lifespan of babies born during that time.

"We show that solar activity (total solar irradiance) at birth decreased the probability of survival to adulthood for both men and women," the researchers write in the journal Proceedings of the Royal Society B. "On average, the lifespans of individuals born in a solar maximum period were 5.2 years shorter than those born in a solar minimum period."

The came to that conclusion by looking at 200 years of demographic data in Norway, around 8,662 births between 1676 and 1878, and measured it against records of sunspots and other solar activity.

Their other finding: Fertility and lifetime reproductive success also took a hit for women born in those years, particularly among those of low social status.

"The proximate explanation for the relationship between solar activity and infant mortality may be an effect of folate degradation during pregnancy caused by UVR (ultraviolet radiation)," the researchers say.

That said, the sun is still a vital source of vitamin D and the right amount of exposure is necessary for a healthy life.

As for the folate degradation mentioned by the scientists, Scientific American's coverage of the study notes the degradation of folate (a form of Vitamin B) may not be as much of an issue today, when supplements are readily available.

And even one of the scientist's authors, Frode Fossøy of the Norwegian University of Science and Technology, doesn't buy the argument that pregnant women should stay out of sun altogether.

"A lot of the media now has been that if you're pregnant or planning to become pregnant, then you should avoid sun, or not go south for the winter to get a lot of sun, especially if you're very pale," he told Scientific American. "We also need sun, to get vitamin D — so it's a delicate balance."

WATCH: Great time lapse of solar and lunar eclipses