The study published last month by Dr Jorge Chavarro's group at Harvard School of Public Health in Boston, Massachusetts, was indeed a 'surprise study' (see BioNews 986) given the plethora of papers showing contradictory effects. The unfortunate fact is that this one study (suggesting that past cannabis use is associated with higher sperm counts) has received huge media interest and may influence men to their reproductive detriment for some time to come.
Despite its large numbers and authorship from a highly esteemed university, it had several major design flaws. The first was the self-reporting of cannabis use with no quantitative drug testing. This left it open to subjective error and perhaps exaggeration. It is very difficult to obtain accurate data about illicit drug use. Even national and European statistics can only identify cannabis usage within the last month or year but not usage per day as would be required to determine a link with spermatogenesis.
In studies from our lab at Queen's University Belfast, we found conversely that cannabis use impaired both sperm counts and function. Taking cannabis, as a one-off dose, regular usage or as an addition to sperm in vitro, decreased motility and inhibited acrosome reactions. Even more seriously, sperm counts dropped irreversibly as the nurse (Sertoli) cells, that help to make sperm, disappeared following short- and long-term exposure to a selective cannabis agonist.
Secondly, in terms of the data generated by the Harvard study, we do not know the baseline of sperm counts before cannabis smoking. This is a fundamental design flaw; making the reported increase unreliable.
A third concern is the impact of confounding factors. Recreational drug users often take cocktails of 'club' drugs. While most recreational drugs have negative impacts on sperm, there are exceptions. Another commonly used drug that impacts directly on sperm is Viagra (sildenafil citrate). We have reported that Viagra can increase progressive motility by both recruiting more sperm and accelerating their movement. It also initiates acrosome reactions. Thus, multi-drug use may account, in part, for these unexpected results.
Recreational cannabis is particularly potent because it deregulates our very sophisticated endocannabinoid system (ECS). This system acts to protect us from stress. It encourages us to eat, to rest and to forget. It is a key player in the multifaceted process of male reproduction; often to inhibit it, since its energy demands are at odds with the wellbeing of the individual. Hence, overloading the system with exogenous cannabis is counterproductive for men wishing to become dads, either now or in the future.
Interestingly, the ECS is so sensitive that marked differences in its activity can be detected in semen of fertile and infertile men. These alterations may also point to new biomarkers to determine male reproductive defects and identify novel targets for therapeutic exploitation of ECS drugs to treat male fertility problems.
There has been a recent explosion of interest in men's health, lifestyle, recreational habits – even in the previously taboo topic of men's sperm quality. I applaud this healthy advance of men sharing their personal lives, as women have done for centuries. However, as men seek to find such information online they must not be misled by incomplete information. I would urge media caution in highlighting isolated findings without providing the context of the plethora of conflicting scientific knowledge.