Factors that Affect Male Fertility—and that Standard Tests Might Miss

By Diana Licalzi, MS, RD, CDCES, July 1, 2020
  • male fertility factors

Male fertility is declining worldwide. Over the past 40 years, sperm count among men in the western hemisphere has decreased by 50%and it continues to fall by an estimated 1.4% each year. [1] Unfortunately, male fertility is often overlooked—some men prefer not to discuss it, and when they do, some standard male fertility tests fail to capture contributing factors (more on this later). Stats show that one-third of all infertility cases are due to male infertility factors.[2] In this article, we will discuss the reasons for the decline in male fertility and science-proven dietary and lifestyle approaches to address it.  

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Semen analysis: only one piece of the puzzle

A couple can be assessed for infertility issues when they fail to conceive after (1) 12 months of unprotected intercourse, or (2) six months if the female partner is older than 35. A standard fertility assessment for a man includes a semen analysis, which measures sperm count, morphology (their shape), and motility (the degree to which they move around).

Though men are often led to believe that a normal semen analysis clears them of fertility issues, many prominent experts argue that these current standards don’t always give an accurate or complete depiction of the problem, as they fail to capture many contributing elements of male infertility.[3] That is, they assess the outcome, but not the causes. And this shortcoming is critical, as around 30% of male infertility issues are due to idiopathic sperm abnormalitiesmeaning they are of unknown origin![4] Simply put, current male fertility assessments don't always get to the root of the problem. But luckily, lots of research exists on the impact of lifestyle factors on male fertility—so you have some actionable steps to take to address any fertility issues.


  • Contributors to male infertility


Male infertility is often due to complicated medical factors like genetic mutations, uncontrolled diabetes, or medications.[3] But there are also lifestyle and dietary choices you can make without medical advice to support fertility. First, obesity significantly contributes to reduced male fertility. One meta-analysis of 30 studies concluded that obese men had higher levels of infertility, even if they had normal semen analysis results. This effect has multiple factors—increased body fat causes hormonal dysregulation, increases estrogen production, and can cause damage to sperm’s DNA and mitochondria. Furthermore, other obesity-related conditions like insulin resistance and erectile dysfunction may negatively affect fertility. And sleep apnea, another common symptom of obesity, impacts nocturnal testosterone rhythm which may lower fertility levels.[5]

causes of male fertillity

Oxidative stress

Oxidative stress is a result of an imbalance between reactive oxygen species (ROS) and antioxidants in the body. ROS—sometimes called "free radicals"—are molecules that easily react with other molecules. A buildup of ROS and these cellular reactions can cause damage to cells, proteins, and DNA in the body. Antioxidants, on the other hand, help to neutralize ROS, negating their detrimental effects. A pro-inflammatory diet (i.e. the standard American diet), stress, and environmental toxins, among other factors, all contribute to an imbalance between these two groups of molecules. Over time, oxidative stress can lead to accelerated aging and the development of many chronic illnesses. And fertility is not exempt from these effects—studies show that oxidative stress causes damage to sperm’s DNA and may decrease sperm motility.[6] 


Other lifestyle factors

Additional influences that may affect male fertility include vitamin D deficiency, stress, excessive caffeine and alcohol intake, and excessive physical activity, particularly cycling. [7-8] Interestingly, marijuana use also seems to play a role in fertility, though not in a consistent way. Marijuana abuse negatively affects spermatogenensis, but preliminary evidence shows that moderate use is associated with a higher sperm concentration.[9] When looking at couples undergoing fertility treatments, research demonstrates a higher live birth rate when the male was a marijuana smoker, but higher pregnancy losses when the woman was a smoker [10]. 


Ways to improve male fertility

Weight loss and exercise

Though the literature on weight loss for fertility is still young, some studies have found that losing weight and lowering BMI may reduce oxidative stress and lessen DNA damage in sperm.[11] Exercise can also help! A randomized controlled trial of 90 obese adults assessed the effect of a 16-week exercise intervention on male fertility. After completing aerobic training three times per week for the duration of the study, the intervention group showed significantly increased sperm count motility, morphology, and testosterone compared to control.[12]


Dietary habits 

Research shows that improving dietary habits can also improve fertility in men. When examining the dietary patterns of 129 male partners of pregnant women, researchers found that “strong adherence to a healthy dietary pattern (defined as a diet rich in grains, fruits, legumes, vegetables, and olive oil) is associated with better semen quality.”[13] In addition, key findings from a 2017 systematic review of 23 observational studies showed that sperm motility was positively related to fruit and vegetable intake, especially dark green vegetables. Processed meat and saturated fat were negatively associated with sperm parameters, both trans and saturated fat negatively affected count and concentration of semen, and motility was inversely associated with intake of sugar-sweetened beverages.[14] 

Now, we can’t talk about male fertility without talking about nuts (we just couldn't help ourselves). Nuts are rich in a variety of nutrients including omega-3 fatty acids, folate, plant-based protein, healthy fats, and fiber. Studies show that nut intake may improve numerous sperm parameters including total count, vitality, motility, and morphology.[15]  

vitamin d phone

Vitamins, minerals, and supplementation

Currently, there isn’t enough research to recommend supplements specifically for male fertility. However, this review showed that antioxidant supplements may improve semen parameters in infertile men. The most effective supplements were vitamin C, vitamin E, CoQ10, or a combination of the three.

Lastly, low testosterone levels may reduce sperm production, so optimized blood testosterone levels may also improve fertility. Studies show that both vitamin D and magnesium can support healthy testosterone levels, so be sure to monitor all three biomarkers through periodic blood testing.[16-18]


A summary of male infertility

  • Male fertility has been declining worldwide. 
  • Factors affecting male fertility may not always be identified in a standard semen analysis.
  • Obesity, oxidative stress, a sedentary lifestyle, and vitamin and mineral deficiencies may all contribute to male infertility.
  • A diet rich in plant-based whole foods and low in red and processed meats, saturated fats, and added sugars supports male fertility.
  • Testing and monitoring important biomarkers like testosterone, vitamin D, and magnesium may help aid in increased fertility.
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20170517 Diana Licalzi0312 (1x1)

Diana Licalzi, MS, RD 
  • Diana is a Content Strategist and Team Nutritionist at InsideTracker. As a Registered Dietitian and self-proclaimed "biohacker," Diana enjoys researching and testing the latest trends and technology in the field of nutrition and aging. You'll often find Diana , completing a 24-hour fast, conducting self experiments, or uncovering strategies to increase longevity. Follow her on Instagram at @dietitian.diana.



[1] https://pubmed.ncbi.nlm.nih.gov/28981654/

[2] https://www.nichd.nih.gov/health/topics/menshealth/conditioninfo/infertility

[3] Wright, H. Myth Conception: How Men Can Improve Their Fertility. Lecture, Philadelphia PA. 2019.

[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6524745/

[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4408383/

[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6472207/

[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5826784/

[8] https://pubmed.ncbi.nlm.nih.gov/29774489/

[9] https://academic.oup.com/humrep/article-abstract/34/9/1818/5549505

[10] https://academic.oup.com/humrep/article-abstract/34/4/715/5307080

[11] https://pubmed.ncbi.nlm.nih.gov/29388233/

[12]  https://pubmed.ncbi.nlm.nih.gov/28627195/

[13 https://pubmed.ncbi.nlm.nih.gov/28292616/

[14] https://pubmed.ncbi.nlm.nih.gov/29266782/

[15] https://academic.oup.com/ajcn/article/108/5/953/5201549

[16] https://pubmed.ncbi.nlm.nih.gov/21675994/


[18] https://pubmed.ncbi.nlm.nih.gov/21154195/

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