Light pollution is not just bad for the environment, but it also throws off the reproduction cycle in nocturnal lemurs, according to a new study.

French scientists have shown that light pollution can override the natural reproductive cycle of some animals, making them sexually active out of season.

"The natural light/dark cycle allows living organisms to time a variety of behavioral and physiological rhythms, including migration, accumulation of reserves, dormancy and reproduction," lead author Thomas Le Tallec explained in a press release.

For mouse lemurs, they are sexually inactive during the winter, but during the summer months when they can enjoy 12 hours of sunshine, their libidos are up. To test just how sensitive these animals are to light, over a five-week period during midwinter researchers placed sexually inactive male lemurs inside special climate chambers where the level of light was controlled by fluorescent lamps.

In the control group, the level of light at night was set to only equal that of the full moon. The second group was exposed to yellow LED lights to mimic streetlights. After only two weeks, the light-pollution group had considerably larger testes and higher levels of testosterone than the control group.

The research team believes the light-sensitive hormone melatonin explains their sensitivity to light in terms of their reproduction cycle. Melatonin can only be produced in darkness so that in long-day breeders, such as mouse lemurs, high melatonin levels in winter normally repress sexual activity. When darkness is breached by light pollution, however, melatonin production is inhibited.

The scientists also claim that their study possibly indicates that light pollution not only affects animals in this way but also humans.

"We postulate that chronic exposure to light pollution could impact the human reproductive function as well. Night work and artificial light are associated with menstrual irregularities, decreased fertility, spontaneous abortions and pre-term births. However, this is only a hypothesis and rigorous studies are needed," Le Tallec concluded.

This research was presented at the Society for Experimental Biology Annual Meeting 2014 held at Manchester University, UK, from the July 1-4.