Men may want to reconsider how closely they store their mobile phone to the family jewels.

A meta-analysis of ten past studies, led by researchers at University of Exeter, U.K., found a small but consistent drop in sperm quality if the men (or their, uh, samples) had been exposed to mobile phone radiation. While researchers found no link between mobile phone radiation and an actual drop in fertility rates, the finding could contribute to understanding the global -- and still unexplained -- drop in sperm count.

"The implications are likely to be greatest for subgroups of men with multiple exposures to different factors which act together to affect their sperm; and possibly for men who already have borderline fertility," said researcher Fiona Mathews, Ph.D in an email message to The Huffington Post. "However, we need to remember that sperm quality is very variable naturally, and men with a wide range of ‘motility’ and ‘vitality’ measures can still be considered normal and achieve a pregnancy."

Sperm quality is usually assessed using three measures in combination: sperm motility -- a measure of the percentage of sperm that are swimming normally; sperm viability -- meaning the percentage of sperm that are alive in a given sample; and sperm concentration, meaning the density of sperm in fluid.

Mathews analyzed ten studies that included 1,492 total samples and ranged from experimental lab studies with sperm samples to observational studies in humans. She found that in both types of studies, exposure to the radio-frequency electromagnetic radiation from mobile phones was associated with an average 8.1 percent decrease in sperm motility and an average 9.1 percent decrease in sperm viability. The link between radiation and sperm concentration was more ambiguous and varied depending on how researchers chose to analyze results. A simple analysis suggested sperm concentration did decrease, but more sophisticated analyses suggested there was no significant change.

Optimal levels for healthy sperm vary, but the World Health Organization's 2010 analysis found that in a study of men around the globe, 15 million sperm per milliliter was considered typical for fertile couples (defined as conception within 12 months of trying). The fertile men also had at least 58 percent vitality, 40 percent motility and at least four percent were normal-shaped sperm cells.

However, just because a man has a low sperm count doesn't necessarily mean that he and his partner can't conceive naturally. After all, it only takes one sperm cell to fertilize the egg cell. And while the meta-analysis does show a decrease in sperm quality linked to mobile phone exposure, it doesn't necessarily mean that the men were any less fertile. It does, on the other hand, point to a need for greater research to explore the meaning of this link.

"I would not argue that use of a phone is going to suddenly make men infertile," said Mathews. "However, given the increasing use of wireless devices, and general declines in sperm quality seen over the last 10-20 years across the developed world, this is certainly an area that is in urgent need of research."

Jamie Grifo, M.D., Ph.D. and program director of the NYU Fertility Center, was not involved with the analysis but praised Mathews' work for giving exposure to new avenues of research on fertility. However, he did point out some important caveats -- namely, that the analysis didn't necessarily show cause and effect, and that there was no link to an actual decrease in fertility.

"I wouldn't throw away my cell phone based on this study," said Grifo in a phone interview with HuffPost. "There's a lot of anxiety about fertility, and this study doesn't give us cause for great worry." Still, he had some advice for men who are concerned about their fertility based on this study.

"Don't ditch your cell phone, but be smart in how you use it -- don't put your cell phone in your front pocket," Grifo suggested. Mathews echoed this advice, based on her findings.

"Altering where you keep your mobile phone is a fairly easy lifestyle change to make, and certainly will do men no harm," Mathews wrote. She also emphasized that scientists have already identified several factors that affect sperm health. She advised men to keep things loose and cool down there by wearing loose-fitting underwear and avoiding activities that keep genitals overheated for a long amount of time.

Other recent studies show that stress is associated with lower sperm concentration, while chemicals in many household items also have a negative effect on sperm function.