Suspected drop in male fertility rates prompts search for answers; new clinical and mouse studies should encourage clinical research
by Craig Weatherby
Are American men—or any others—becoming less fertile?
Some studies suggest that male fertility rates have fallen, especially in England and northern Europe.
And in theory, the toxins and endocrine-disrupting chemicals people get from food, air, and water could cause fertility to fall in either or both sexes.
Some hormone researchers assert that such chemicals have caused male fertility rates to drop by some 30 percent over the past several decades.
Iranian group found low omega-3 levels in the sperm cells of infertile men... and a high, American-style ratio of omega-6 to omega-3 fats.
Mice deficient in omega-3 DHA show sperm abnormalities and low sperm counts; problems were reversed by feeding them DHA.
Evidence for changes in male fertility rates remains murky; either historical or current rates have been misreported, or there's been a real drop, likely induced by stress and/or chemicals.
But while birth rates are down sharply in Europe and Japan, a search of the medical literature yields no clear proof that male fertility rates are dropping there or in the Americas.
Studies have reported finding a drop in fertility rates since the early 20th century, but other researchers say that those claims don’t stand up under close scrutiny.
Nor is it clear whether endocrine-disrupting chemicals or other environmental toxins are causing low sperm counts or weak sperm.
Still, given the steep drop in some nations' birth rates, it's smart to ramp up research on potential fertility factors.
The results of a recent clinical new mouse study could be important... if men's fertility rate has either dropped or starts sliding.
And regardless of broader public health concerns, couples experiencing conception problems need to know whether omega-3s can really help with sperm problems or scarcity.
Clinical study finds low omega-3 and high omega-6 levels in infertile men
An Iranian team reported last year that infertile men had lower levels of omega-3 fatty acids in their sperm, compared with fertile men (Safarinejad MR et al. 2009).
And they made another very important discovery: the ratio of omega-6 to omega-3 fatty acids was significantly higher in infertile men compared to fertile controls, and men’s sperm count fell as the omega-6/omega-3 ratio rose.
That study involved 150 men and as the authors wrote, “To our knowledge, this is the first study evaluating the association of omega-3 and omega-6 fatty acids on semen quality...”
This adds infertility to the growing list of problems associated with the “omega imbalance” in then American diet, caused by the lack of fish or fish oil, and an excess of omega-6-rich vegetable oils (corn, soy, safflower, canola, cottonseed, sunflower).
The authors went on to note the obvious: “These results suggest that research should be performed to assess the potential benefits of omega-3 fatty acid supplementation as a therapeutic approach in infertile men.”
Mouse study sees dramatic effect from omega-3 DHA
In a related investigation, researchers from the University of Illinois used mice genetically engineered to lack DHA (Roqueta-Rivera M et al. 2010).
DHA is one of the two key omega-3 fatty acids found in fish fat and in human cell membranes… including the membranes of sperm cells.
The Illinois team engineered mice to lack a gene which enables production of the enzyme (delta-6-desaturase) needed to convert the short-chain, plant-source omega-3 called ALA into long-chain omega-3 DHA.
The DHA-deficient mice were found to have fewer sperm… and more sperm abnormalities in what little sperm they did have.
“In the absence of DHA, male mice are basically infertile, producing few if any misshaped sperm that can't get where they need to go,” said lead researcher Dr. Manabu Nakamura (IU 2010).
“We looked at sperm count, shape, and motility and tested the breeding success rate, and the mice lacking DHA simply were not able to breed,” added Manuel Roqueta-Rivera, a doctoral student who also worked on the study. (IU 2010)
In the DHA-deficient mice, sperm counts were extremely low. The sperm that were produced were round instead of elongated, and were unable to move well.
When mice were fed a diet supplemented with 0.2 percent DHA, the researchers found that the fatty acid restored “… all observed impairment in male reproduction”.
As Dr. Nakamura said, “It was very striking. When we fed the mice DHA, all these abnormalities were prevented.”
But he sounded a note of caution, saying, “…we're still at the starting point in understanding the mechanisms that are involved, and we need to do more research at the cellular level.”
The Illinois researchers intend to continue to explore the ways in which omega-3s affect fertility… stay tuned.
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- Foster WG, Neal MS, Han MS, Dominguez MM. Environmental contaminants and human infertility: hypothesis or cause for concern? J Toxicol Environ Health B Crit Rev. 2008 Mar;11(3-4):162-76.
- Joffe M. What has happened to human fertility? Hum Reprod. 2010 Feb;25(2):295-307. Epub 2009 Nov 19.
- Roqueta-Rivera M, Stroud CK, Haschek WM, Akare SJ, Segre M, Brush RS, Agbaga MP, Anderson RE, Hess RA, Nakamura MT. Docosahexaenoic acid supplementation fully restores fertility and spermatogenesis in male delta-6 desaturase-null mice. J Lipid Res. 2010 Feb;51(2):360-7. Epub 2009 Aug 18.
- Safarinejad MR, Hosseini SY, Dadkhah F, Asgari MA. Relationship of omega-3 and omega-6 fatty acids with semen characteristics, and anti-oxidant status of seminal plasma: a comparison between fertile and infertile men. Clin Nutr. 2010 Feb;29(1):100-5. Epub 2009 Aug 8.
- Sallmén M, Weinberg CR, Baird DD, Lindbohm ML, Wilcox AJ. Has human fertility declined over time?: why we may never know. Epidemiology. 2005 Jul;16(4):494-9.
- Stroud CK, Nara TY, Roqueta-Rivera M, Radlowski EC, Lawrence P, Zhang Y, Cho BH, Segre M, Hess RA, Brenna JT, Haschek WM, Nakamura MT. Disruption of FADS2 gene in mice impairs male reproduction and causes dermal and intestinal ulceration. J Lipid Res. 2009 Sep;50(9):1870-80. Epub 2009 Apr 7.
- University of Illinois at Urbana-Champaign (UI). Lack of omega-3 fatty acid linked to male infertility. Accessed at http://www.eurekalert.org/pub_releases/2010-04/uoia-uoi_1041210.php