Extensive research highlights effect of diet on sperm quality

The global decline in semen quality and the declining birth rates in the west is a matter of serious concern. This decline has been ongoing since the 1940’s and has accelerated since the 1970’s. Based on a study¹ of 185 countries from 1973-2011, it has been estimated that sperm quality has fallen by 50-60%.

In addition to the decline in sperm quality, some researchers have also reported a long-term reduction in serum testosterone levels².  It is unclear, specifically, what factors are driving this trend towards poorer quality sperm and declining testosterone levels.  However, potential explanations tend to fall into two categories:

Environmental factors

These include exposure to endocrine-disrupting chemicals, and the potential effects of air/water pollution³

Behavioural factors

These are largely driven by lifestyle and include patterns of smoking, alcohol intake and nutrition.³

In terms of nutrition as a behavioural factor, diet may play a role in testicular function but data on how dietary patterns influence testicular function are somewhat lacking.

Key studies include:

A 2017 systemic review found that a healthy diet, rich in certain nutrients such as Omega-3 (ѡ-3) fatty acids, antioxidants and certain vitamins and low in saturated fatty acids/trans-fatty acids, was associated with good semen quality.⁴

A 2018 review highlighted that a diet that included regular helpings of fish, shellfish, poultry, cereals, vegetables and fruit was associated with healthy semen parameters.⁵

A 2010 review suggested that Vitamin A could be useful in generating healthy sperm.⁶

Two previous studies in 2017 and 2018 investigated the potential role of supplementation with ω-3 fatty acids on semen parameters ^{7, 8} `Both of these studies associated higher sperm concentration, total sperm count and motility with ⍹-3 fatty acid supplementation.

Supplementation with ω-3 fatty acids and diet modification both appear to show some promise in terms of maintaining testicular health and the generation of healthy sperm. Two more recent studies published this year reinforce these findings.

⍵-3 fatty acids and semen quality: a contemporary Danish study

In Denmark, researchers at the University of Southern Denmark recruited 1,679 young men (median age: 18.9 years) into a questionnaire-based study⁹ between 2012 and 2017.

The aim of this study was to determine if intake of ω-3 fatty acid supplements is associated with testicular function as measured by semen quality and reproductive hormone levels among healthy men.

With this in mind, the men answered a questionnaire, underwent a physical examination and provided blood and semen samples.

In the study semen quality was defined in terms of volume, concentration, total sperm count, percentage of morphologically normal spermatozoa and motility. Serum reproductive hormone levels were measured as follicle-stimulating hormone, luteinizing hormone, testosterone, free testosterone and inhibin B levels.

The main findings of this study were as follows:

• 8% (98) had taken fish oil high in ⍹-3 fatty acids in the previous three months to the day of examination, of which 54% reported intake on more than 60 days
• Men with fish oil intake on more than 60 days had higher semen volume (0.64 ml more) than the control group
• Testicular volume was greater in the fish oil group (by an average of 1.5 ml)
• Men with fish oil supplement intake had a 20% (95% CI, 9%-31%) lower follicle-stimulating hormone level and 16% (95% CI, 8%-24%) lower luteinizing hormone level compared with men with no supplement intake.

The authors wrote, “These findings suggest that intake of fish oil supplements was associated with better testicular function, which is less likely to be due to confounding by indication, as no associations of intake of other supplements with testicular function were found.”

Diet and testicular function

The same Danish team, in a separate study also published this year, investigated whether adherence to specific dietary patterns is associated with testicular function in young men¹⁰.

This study included 2,935 young men (median age: 19 years) who were enrolled between 2008 and 2017 to take part in a questionnaire-based assessment together with semen tests, blood tests and physical examination (ultrasound to measure testicular volume).

In terms of dietary patterns four types of diet were distinguished:

• Western: characterized by greater intake of pizza, French fries, processed and red meats, snacks, refined grains, sugar-sweetened beverages and sweets
• Prudent: characterized by greater intake of fish, chicken, vegetables, fruit and water
• Open-sandwich (a traditional Danish eating pattern): characterized by greater intake of cold processed meats, whole grains (primarily whole-grain breads), mayonnaise, cold fish, condiments and dairy
• Vegetarian-like: characterized by intake of vegetables, soymilk, and eggs and avoidance of red meats and chicken.

Key findings of this study included:

• The greatest adherence to the prudent diet pattern was associated with the highest total sperm count (median, 167 million)
• Adherence to the western pattern was associated with the lowest total sperm count (median, 122 million)
• Adherence to the vegetarian-like pattern (median, 151 million) and open-sandwich pattern (median, 146 million) yielded similar sperm counts
• Men with the highest adherence to the Western pattern had a lower median ratio of inhibin B to follicle-stimulating hormone and higher median ratio of free testosterone to luteinizing hormone, compared with men with the lowest adherence to this pattern.

The authors concluded, “Adherence to generally healthy diet patterns were associated with better semen quality, with potentially more favourable fertility potential among adult men.“

Both these studies reinforce previous findings that diet, and dietary adherence seem to play a role in testicular health and in the creation of healthy sperm. In addition, although the results are not conclusive, it appears that a dietary supplement of fish oil (⍵-3 fatty acids) may also potentially be of some benefit in maintaining higher semen quality.