For several decades now, numerous studies have suggested that moderate alcohol consumption increases longevity by protecting against cardiovascular disease, and more recent investigations have linked a few tipples per week with a reduced risk of diabetes. Yet at the same time, other research has found associations between light to moderate drinking and both neurological decline and various types of cancer – leaving those concerned about making the right lifestyle choices (or those hoping to defend what they plan to keep doing anyway) pretty confused.

Another aspect of health with contradictory results about alcohol? Male fertility.

A new study published in the journal Andrology revealed that men who consumed 4 to 7 units (1 unit = 12.5 g of ethanol, which corresponds to 125 mL wine, 330 mL beer, or 30 mL spirits) per week had greater semen volume and total sperm count compared with those who drank between less than one unit and three units per week.

Similar to examinations on heart health and overall mortality, the team found a U-shaped association between alcohol and sperm concentration, meaning that men who drank very little and those who regularly binged tended to have no-to-low benefit whereas those in the middle showed a notable benefit.

The semen samples analyzed in this work came from 323 men, who, alongside their female partner, were undergoing assisted reproductive technology testing and treatment at an infertility clinic in Italy. Some men in the cohort had sperm issues and some were normal. The researchers adjusted their statistics for such fertility problems and other factors known to influence sperm quality and production: age, BMI, physical activity level, caffeine consumption, smoking status, and days of abstinence before sample collection.

Interestingly, the pattern of better semen quality among moderate drinkers was even seen in men with fertility problems.

Lead author Dr Elena Ricci and her colleagues highlight several proceeding studies with opposing findings, most notably a large 2014 study that concluded alcohol consumption begins to adversely affect sperm quality at levels equaling 5 or more units a week, though the association is strongest in men who drink 25 more units.

They speculate that the inconsistencies between findings could stem from differences in how studies categorize alcohol consumption and to the different drinking habits of the populations studied. For example, many alcohol-health investigations that include teetotalers could have skewed results because these subjects avoid alcohol due to the ill effects of past drinking (the "sick-quitter hypothesis").

As for the biochemical mechanism linking alcoholic beverages and fertility, the team identified possibilities going in both directions.

“A relation between alcohol drinking and semen parameter is biologically plausible. It is known that beer and wine contain polyphenols such as resveratrol or xanthohumol, which were demonstrated to have a strong therapeutic and cell protective potential,” the study authors explained.

“On the other hand, different studies experimentally proved that alcohol has a detrimental effect at all levels of the male reproductive system: it interferes with the function of the hypothalamic-pituitary-testicular axis, impairing gonadotropin secretion with consequent decreasing of testosterone levels.”