What are the causes and treatments of infertility?

Infertility occurs when natural conception (pregnancy) cannot occur. Just over 15% of couples have trouble conceiving and many single or single-sex couples also cannot conceive. In heterosexual couples there are two types of infertility, primary (no previous children) and secondary (previous conceived children) and infertility is usually diagnosed after a year of unsuccessful attempts at conception or six months if the female is over 35 years of age.

Infertility affects millions of people of reproductive age across the globe. It can have severe consequences on an individual’s sense of self, future aspirations and families and relationships. One-third of the causes of this infertility are due to the female, one third due to the male and one third due to unknown causes.

What is fertility?

Fertility is when an egg and sperm join in conception in order to fertilise a female egg, which is implanted in the female womb lining and develops into an embryo or baby. This requires healthy male sperm to be ejaculated or injected into a healthy egg, either via a test tube insemination or via sexual intercourse via the fallopian tubes.

Egg and womb lining development is under the control of the female hormones FSH (follicle stimulating hormone), LH (luteinising hormone), Oestrogen and Progesterone. FSH is produced by the pituitary gland and causes the egg to mature in the ovary and stimulates the ovaries to release Oestrogen. Oestrogen is produced by the ovaries and repairs and thickens the uterus lining and stimulates LH release. LH is produced by the pituitary gland and triggers the release of the egg at day 14 of the menstrual cycle and Progesterone is produced by the ovaries and maintains the uterus during the middle part of the menstrual cycle and during pregnancy. If a woman becomes pregnant, the placenta produces Progesterone to support the development of the baby and prevent miscarriage. Testosterone is also needed in females for breast development

Most males have two testes. The testes make the hormone Testosterone in response to LH. FSH stimulates testicular growth and sperm cell development. Testosterone is required for the development of male sexual characteristics. It also triggers the production of sperm from the vas deferens in the scrotum. When sperm is ejaculated during sexual arousal or intercourse, it joins with a lubricating liquid and becomes semen. Oestrogen is also needed by males for healthy sperm development, the ability to have an erection, and sex drive (libido).

Male infertility is usually due to issues with sperm count, Testosterone levels or ejaculation malfunction. Testosterone naturally decreases as men age, while Oestrogen hormone levels increase, and so though men can have children later in life than females, age is still a limitation for healthy conception. The older you are, the less likely you are to have healthy offspring.

What causes infertility?

Female infertility can occur at any stage of the pregnancy process. Female hormonal problems and problems with the womb or fallopian tubes are very common causes of female infertility. As a woman ages, her FSH and Oestrogen levels diminish, and her egg stores and health are reduced. Over the age of 35, the fertility rate decreases by up to half compared to that of age 25. Diabetes, eating disorders such as anorexia and bulimia and obesity, overexercising and stress also reduce hormonal levels.

Sex-hormone-synthesis-Diotel et al, 2018- Laura Campbell
Figure 1: Female and male sex hormone production. Diotel et al, 2018

Oestrogen and Progesterone are made of cholesterol. Cholesterol is converted to Pregnenolone and this is converted to either Progesterone or DHEA (Dehydroepiandrosterone) which is converted into Oestrogen and Testosterone (both females and males have Oestrogen and Testosterone as they are needed for fertility and bone health but to varying levels). Therefore a diet too low in dietary cholesterol, or a body too athletic (so all the body fat is turned to muscle) in men and women (such as in long distance runners or body builders), has insufficient body fat levels to make these key hormones. Low body fat can also cause body temperature to decrease, as food is needed for energy including thermodynamic energy, heating the body. Body fat is also needed for heat insulation, and therefore a low body weight causes a low body temperature which can cause testes scrotal hypothermia, decreasing sperm count.

A high-stress lifestyle also reduces Oestrogen, Testosterone and Progesterone levels. This is because of the “flight and fight” mechanism. The human body was built to survive, and as such to protect humans from stressors, or threats. This means that it prioritises defence from stress over all other body mechanisms. Therefore, an acute stressful situation or chronic pre-apprehensive stress (anxieties and worries) puts the body in defence mode and deprioritises the digestive (food breakdown and nutrient absorption), immune (defence against disease) and reproductive (sexual) systems. In this reprioritisation, the DHEA made from the cholesterol is converted to Cortisol stress hormone instead of Oestrogen and Testosterone. This process is called “Cortisol steal” in medicine. Therefore, stress and anxiety diminish Oestrogen and Testosterone levels. For those suffering from infertility, measures to reduce environmental or mental stressors (worries) in both the female and male, must be taken to improve hormone health.

Other causes of infertility include obesity as increased fat cells (adipocytes) and raised blood glucose levels (insulin resistance due to too high dietary sugar and fat) cause levels of Oestrogen to increase and decreased Progesterone and Testosterone production. In males, this can cause erectile dysfunction and a low sperm count. High Oestrogen can also cause impotence in men. Obesity also increases body temperature (as we eat for energy and for thermogenesis, to heat our bodies and body fat provides insulation). High testes' temperature can cause scrotal hyperthermia, decreasing sperm count. Increased adipocytes also increase body inflammation increasing sperm DNA fragmentation and decreasing sperm health. Therefore, obesity is a major cause of infertility in men.

Just as having too low Oestrogen in females can cause infertility, too high Oestrogen is also unhealthy as it causes a process called Oestrogen dominance, which stops the egg being released in the menstrual cycle. Low Progesterone levels can also prevent womb development, preventing the implantation of an egg and development of an embryo, and causing miscarriage. Obesity also puts females at higher risk of polycystic ovaries (PCOS) and ovarian cysts, which are other major causes of infertility.

Other causes of infertility include substance abuse, smoking, diabetes, sexually transmitted diseases, and genetics. Thyroid disease can also cause infertility. Thyroid hormone is needed for metabolism and both hyperthyroidism (too much thyroid hormone) and hypothyroidism (too little thyroid hormone), can influence fertility by affecting ovulation (the release of the egg) and menstrual cycle in females and affecting sperm count in males.

Kidney disease also disrupts hormone levels and can cause increased LH levels in men, reducing sperm count overall, and decreased LH in females, disrupting the menstrual cycle egg release. Blocked fallopian tubes in the womb, pelvic inflammatory disease, celiac disease, and ovarian or testicular cancers, also cause infertility. High heat exposure from tight clothing or frequent use of saunas, also decreases sperm count.

How do I increase my fertility?

A good way to start improving fertility is to reduce stress to both males and females. This can be incredibly hard if you are going through the anxiety and stress of fertility treatment but is essential to improve hormone regulation. Stress also impacts sleep and appetite which themselves impact stress levels. Oestrogen is a mood stabilizer and so the more stressed you are, the more stressed you are likely to become. Activities to reduce stress are essential when attempting to conceive.

Maintaining a healthy body fat percentage in both males and females is also essential for fertility. Too high body weight causes Oestrogen dominance which causes infertility and too low body weight causes low Oestrogen levels, which causes infertility. This is not about weight, but body fat, as a very muscular man may still suffer infertility due to a low body fat percentage.

Diet is also very linked with fertility, though it must be tailored and personalized to your body. Dietary saturated fat is necessary for hormone production as hormones are made of Cholesterol. Too much dietary saturated fat causes Oestrogen dominance, and therefore to increase fertility it would be advised to consume more “healthy” fats such as monounsaturated fats in nuts and seeds, fish and olive oil and lots of dietary fibre from vegetables, which decrease LDL Cholesterol (low density lipoprotein) levels and decrease saturated fat levels.

Too little saturated fat in your diet causes low Oestrogen levels, and so a diet rich in Cholesterol saturated fat, such as fatty meat, butter, full fat dairy, eggs, coconut oil and processed foods, increases LDL cholesterol and increases body saturated fat. This is counterculture (which promotes Cholesterol reducing foods to promote heart health in the obesity epidemic) but is necessary for those underweight or too muscular for fertility.

In overweight men and women, a diet high in fibre and complex (vegetable-based) carbohydrates and high in monounsaturated fats, omega-3 and B vitamins, is associated with decreased LDL levels and decreased Oestrogen levels, improving fertility. In underweight individuals, a diet high in fat and low in carbohydrates is necessary to increase Oestrogen levels. Both folic acid (B9) and vitamin D have been shown to increase fertility and a diet high in antioxidant anti-inflammatory foods improve sperm count and egg quality.

Alcohol also reduces fertility. It is a toxin that must be broken down by the liver. Even moderate alcohol consumption has an effect as the liver prioritizes the breakdown of toxins over the breakdown of Oestrogen. Oestrogen must be broken down after day 14 of the menstrual cycle. It is the decrease in plasma (blood) Oestrogen and LH peak that triggers the egg release (ovulation). If Oestrogen levels do not fall, the egg is not released (anovulation) and LH levels are elevated. This has a contraceptive effect. Chronic heavy alcohol use can diminish ovarian reserves. In males, the increased plasma Oestrogen causes hypoestrogenism, Oestrogen dominance which causes decreased testosterone and sperm production in males.

Smoking and drug use (even CBD oil) and even some medications are also toxins which are broken down by the liver. Smoking has been found to decrease sperm volume, total sperm count, semen volume and sperm motility in men. In females, it causes the same effects as alcohol.

Regular exercise also improves fertility, but not to extremes. This is because exercise can help those overweight to lose weight. In those at a healthy weight, it can reduce stress and cortisol levels and improve insulin levels. However excessive exercise can cause the ratio of body muscle: fat to increase in favour of muscle, reducing body fat and decreasing Oestrogen (athletes triad) in females. Regular moderate exercise improves fertility.


  1. Diotel, N., Charlier, T.D., Lefebvre d’Hellencourt, C., Couret, D., Trudeau, V.L., Nicolau, J.C., Meilhac, O., Kah, O. and Pellegrini, E., 2018. Steroid transport, local synthesis, and signaling within the brain: roles in neurogenesis, neuroprotection, and sexual behaviors. Frontiers in neuroscience, p.84.

Copyright Laurentia Laura Campbell 11/05/2022



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Laurentia (Laura)Campbell

Laurentia (Laura)Campbell

Neuroscience, mental health and nutrition academic and writer. Life-experimenter, trying to add value with an insatiable appetite for actioning positive change.