The sun's rays may shape human lives in a surprising way: High levels of sun exposure during the year of birth may increase infant mortality and shorten the average life span of a population, a new study finds. 
 
 Researchers looked at people in Norway who were born over two centuries, and compared those who were born during years of peaks in solar activity with those born during years of the lowest levels of solar activity. Results showed that people born during solar peaks lived 5.2 years less, on average, than individuals born in years with the lowest solar activity. 
 
 Exactly how the sun's activity at the time of a person's birth may affect life span isn't known. But peak solar activity brings higher levels of ultraviolet radiation to Earth, and some evidence suggests that UV radiation may increase infant mortality by degrading folic acid, or vitamin B9, which is important for the rapid cell division and growth that happen during pregnancy. 
 
 The upshot is, "if you are pregnant, don't get a tan," said Gine Roll Skjærvø, a biologist at the Norwegian University of Science and Technology in Trondheim, Norway, and co-author of the study published today (Jan. 6) in the journal Proceedings of the Royal Society B. "The best time for conception [would] be when there's lower ultraviolet radiation." [11 Big Fat Pregnancy Myths] 
 
 Here comes the sun 
 
 Scientists have long known that ultraviolet (UV) light can affect the development of living organisms by suppressing molecular and cellular processes. The effects of UV radiation on the health and reproduction of aquatic animals are well known, but only a handful of studies have looked at the effects on the human life span or on survival rates of human infants. 
 
 In the new study, Skjærvø and her colleagues examined demographic data from more than 9,000 people born in Norway between 1676 and 1878. The researchers compared the data with historical evidence of cycles of solar radiation compiled by the U.S. National Oceanic and Atmospheric Administration (NOAA). 
 
 Solar activity is measured as the number of dark patches, called sunspots, observed on the sun's surface. This activity varies according to a cycle that lasts about 11 years (although the length varies). Within an average cycle, there are eight years of low activity (known as the solar minimum) followed by three years of high activity (the solar maximum). [Photos: Sunspots on Earth's Star] 
 
 The researchers found that people who were born during the years of high solar activity were less likely to survive to adulthood, with a high percentage of those deaths occurring before age 2. 
 
 In addition, among women born in years of high solar activity, those who had lower incomes (and who likely would have spent more time outside, exposed to the sun) had lower fertility rates and fewer children who survived to age 20, compared with wealthier women, Skjærvø said. 
 
 Too much UV? 
 
 The study shows only a correlation between solar activity and life span; it does not show causation. However, the researchers were able to rule out other explanations for the findings, including socioeconomic status, birth cohort (people born in the same year) and ecology. 
 
 It's impossible to rule out all possible factors, Skjærvø said, but the fact that the effects were seen over hundreds of years suggests that the sun's periodic flare-ups were the likeliest cause of the shortened life spans and reduced fertility. 
 
 Mark Lucock, a nutritional geneticist at the University of Newcastle in Australia, who was not involved in the research, told Live Science the study is "a fascinating piece of work that provides further supporting evidence that early-life environmental factors help shape [human traits] in ways that have long-term consequences."Lucock and his colleagues previously found that exposure to some sunlight during the first few weeks after conception may affect levels of folic acid and vitamin D, both of which can influence the survival of embryos and the development of diseases in adulthood. 
 
 Although "getting too much sun in pregnancy may not be good idea," getting some sun may help the body get enough vitamin D, said George Davis, a researcher at the company Psybernetics, Incorporated, in Augusta, Maine, who has also studied the effects of solar radiation on human health. "There's a balance between too much and too little in sunlight. The real question is, what's that magic breakpoint?" 
 
 So what was the solar activity like the year you were born? The recent years with solar maximums were 1957, 1968, 1979, 1989, 2000 and 2013, and the recent years with solar minimums were 1954, 1964, 1976, 1986, 1996 and 2008. 
 
 Follow Tanya Lewis on Twitter. Follow us @livescience, Facebook & Google+. Original article on Live Science. ||||| The Sun by the Atmospheric Imaging Assembly of NASA's Solar Dynamics Observatory. Credit: NASA Could the Sun be your lucky—or unlucky—star? In an unusual study published Wednesday, Norwegian scientists said people born during periods of solar calm may live longer, as much as five years on average, than those who enter the world when the Sun is feisty. 
 
 The team overlaid demographic data of Norwegians born between 1676 and 1878 with observations of the Sun. 
 
 The lifespan of those born in periods of solar maximum—interludes marked by powerful flares and geomagnetic storms—was "5.2 years shorter" on average than those born during a solar minimum, they found. 
 
 "Solar activity at birth decreased the probability of survival to adulthood," thus truncating average lifespan, according to the paper published in the journal Proceedings of the Royal Society B. 
 
 There was a stronger effect on girls than boys, it said. 
 
 The Sun has cycles that last 11 years, give or take, from one period of greatest activity or solar maximum, to the next. 
 
 Solar maxima are marked by an increase in sunspots, solar flares and coronal mass ejections that can disrupt radio communications and electrical power on Earth, damage satellites and disturb navigational equipment. 
 
 Solar activity is also linked to levels of ultraviolet radiation— an environmental stressor known to affect survival and reproductive performance, possibly by causing cell and DNA damage, according to the study authors. 
 
 Credit: Robert A. Rohde/GNU General Public License 
 
 Fertility reduced 
 
 The team, from the Norwegian University of Science and Technology, based their study on demographic data from church records of some 8,600 individuals from two different mid-Norwegian populations, one poor and one wealthy. 
 
 This was matched to maps of historical solar cycles. 
 
 On top of lifespan, being born in a solar maximum period also "significantly reduced" fertility for women born into the poor category, but not for wealthier women or for men, said the authors. 
 
 "We show for the first time that not only infant survival and thus lifespan but also fertility is statistically associated with solar activity at birth," they wrote. 
 
 It was not clear whether the same would necessarily hold true for people born in the modern era. 
 
 One explanation could be ultraviolet-induced degradation of the B vitamin folate, a shortage of which before birth has been linked to higher rates of illness and death, the team theorised. 
 
 "Our findings suggest that maternal exposure to solar activity during gestation can affect the fitness of female children," the authors wrote. 
 
 "The effect of socio-economic status on the relationship between solar activity and fertility suggests that high-status pregnant women were better able to avoid the adverse effects of high solar activity"—possibly by staying out of the Sun or because a healthier diet curbed the harm. 
 
 The team did not have data about how early or late into a solar maximum event the children were born—a limitation of the study. 
 
 And they could not fully distinguish between pre- or post-natal exposure to ultraviolet light. 
 
 Further investigation is needed, they said, to test whether the results were repeated in people of different skin colours, and those living at different latitudes. 
 
 "This study is the first to emphasise the importance of UVR (ultraviolet radiation) in early life," the authors said. 
 
 "UVR is a global stressor with potential ecological impacts and the future levels of UVR are expected to increase due to climate change and variation in atmospheric ozone." 
 
 Explore further: Suddenly, the sun is eerily quiet: Where did the sunspots go? 
 
 More information: Solar activity at birth predicted infant survival and women's fertility in historical Norway, Proceedings of the Royal Society B, rspb.royalsocietypublishing.or … .1098/rspb.2014.2032 
 
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– If the sun was calm when you were born, you might look forward to a longer life than someone born in a period of high solar activity. The sun's cycles last about 11 years, typically including three years of "solar maximum"—when activity like solar flares, sunspots, and solar storms are at their peak—and eight years of "solar minimum." In a new study in the Proceedings of the Royal Society B, researchers looked at demographic data of Norwegians born between 1676 and 1878, and found that the lifespans of those born during "solar maximum" periods were, on average, 5.2 years shorter than the lifespans of people born during "solar minimum" periods, phys.org reports. "Solar activity at birth decreased the probability of survival to adulthood," thus causing the decrease in average lifespan, the researchers say. A high percentage of the deaths of those born during "solar maximums" occurred by age 2. The authors think ultraviolet radiation is behind the effect. Solar activity is linked to higher levels of UV radiation, which is known to have an impact on survival and reproduction; the authors say there's a possibility that's because it causes cell and DNA damage. There's also evidence suggesting UV radiation degrades vitamin B9, or folic acid—and a shortage of that vitamin before birth has been linked to higher illness and death rates. Interestingly, the study also found that being born during "solar maximum" significantly reduced fertility for women and decreased the number of children they had who survived to adulthood—but only if those women were born into a poor population, suggesting that more well-to-do women may have been better able to avoid the sun or mitigate the sun's harmful effects through a healthier diet. A good rule of thumb? "If you are pregnant, don't get a tan," says one co-author, according to LiveScience. (Another recent study finds that if you feel younger than your age, you'll likely live longer.)