Increased UV radiation can have an effect on human fertility over generations, a new study has warned.
Researchers from the Norwegian University of Science and Technology (NTNU) studied information from more than 9,000 people listed in the church records from 1750 to 1900 in Norway.
Gine Roll Skjaervo found that children born in years with lots of solar activity had a higher probability of dying compared to children who were born in years with less solar activity.
On average, the lifespan of children born in years that had a great deal of solar activity was 5.2 years shorter than other children. The largest difference was in the probability of dying during the first two years of life.
Children who were born in years with lots of sunshine and who survived were also more likely to have fewer children, who in turn gave birth to fewer children than others.
This finding shows that increased UV radiation during years of high solar activity had an effect across generations.
Skjaervo used information on the number of sunspots as an indication of the amount of UV radiation in a given year. The number of sunspots reaches a maximum every 11 years on average, which results in more UV radiation on Earth during years with high sunspot and solar activity.
UV radiation can have positive effects on human vitamin D levels, but it can also result in a reduction of vitamin B9 (folate). It is known that low folate levels during pregnancy are linked to higher child mortality.
The NTNU study showed that families from the lowest socio-economic groups were most affected by UV radiation.
This is probably related to the time period researchers studied, which was a time of clear class distinctions in Norway, especially in rural areas, the study said.
Women who worked in the fields were more exposed to the sun than other women. In many cases they also had a poorer diet.
"There are probably many factors that come into play, but we have measured a long-term effect over generations. The conclusion of our study is that you should not sunbathe if you are pregnant and want to have a lot of grandchildren," said Skjaervo.
The study was published in the Proceedings of the Royal Society B.