Study finds men who smoke weed to be more fertile

It could be that a little bit of pot boosts sperm production a relation that reverses at higher doses.							Getty Images

It could be that a little bit of pot boosts sperm production a relation that reverses at higher doses. Getty Images

Does smoking cannabis affect your fertility?

The study by Harvard T.H. Chan School of Public Health in Boston, USA, involved measuring the sperm count of more than 600 men from couples attending a fertility clinic.

The Harvard researchers collected 1,143 health surveys and semen samples from more than 650 men between the years of 2000 and 2017.

A new study suggests men who have smoked cannabis in the past may have a higher sperm count than men who haven't used the drug.

Overall, a little over half of the men (55 percent) reported ever smoking marijuana in their lifetimes, and 11 percent said that they now smoked marijuana.

When Dr Chavarro compared all the surveys, he found the marijuana users had a common result of having a slightly higher sperm counts and concentration, compared to men who had never used it.

In this study, for instance, cannabis users were also more likely to have higher testosterone levels, which can affect sperm count. Among men who never smoked marijuana, 12 percent had lower-than-normal sperm concentrations.

"These unexpected findings from our study highlight that we know too little about the reproductive health effects of cannabis and, in fact, of the health effects in general, to make strong statements about the impact of cannabis on health, with the possible exception of mental health", said lead researcher Jorge Chavarro, an associate professor of nutrition and epidemiology at Harvard, in a statement.

"Secondly, the study is a great opportunity to spark interest on investigating the health effects of marijuana particularly with the backdrop of increasing legalization of recreational use in the US coupled with a greater perception that marijuana poses no health risks".

The researchers also took blood samples from 317 of the men to assess their hormone levels and found that marijuana smokers had higher levels of testosterone.

They suggest that the association may not show any cause-and effect relationship, but rather reflect the influence of the male hormone, testosterone, on both sperm count and risk-taking behavior, such as smoking cannabis. Along with their medical history, the men were also asked if they had ever used cannabis and, if they had, whether they were still using it.

One explanation is that the men in the study who smoked marijuana already had higher sperm counts than those who did not.

The men were, on average, 36 years old, mostly white and mostly university-educated.

Previous studies - the majority of them in rats, but a few in human males as well - have linked heavy pot use with a slump in sperm production.

Other experts in the field have questioned how robust the association is.

Chavarro also went on to point out that if the study proves anything definitive, it is that the link between marijuana and general health remains something of a grey area.

She said: "Our findings were contrary to what we hypothesised at the start of the study". Many people assume this means the drug is totally safe to use, but scientists are still working out exactly what it does to our bodies.

A normal sperm count is at least 15 million/mL, according to the World Health Organization.