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Unexplained Infertility

There is some research on the impact of the following possibly modifiable life factors and fertility:

Smoking, caffeine and alcohol

Diet, weight and exercise

Exposure to chemicals in food or the environment

Smoking, caffeine and alcohol

High caffeine intake and alcohol consumption (even as few as five drinks a week) have been linked to lower fertility in women. Alcohol can also affect sperm production. Caffeine is found in coffee, cola drinks, chocolate and some over-the-counter medicines.

Components in cigarette smoking can interfere with several aspects of the hormones required in women to both conceive and to establish pregnancy, as well as causing a small increase in the chance of miscarriage. We found two reviews of studies on the fertility of smokers. One concluded that women smoking leads to only a small reduction in their fertility, while the second review suggests that smoking might have a larger impact 51. Women who smoke are also less likely to become pregnant on IVF programs. It is not yet certain whether or not smoking damages sperm quality.

Diet, weight and exercise
Obesity (being very overweight) can negatively affect ovulation and response to infertility treatment (as well as subsequent pregnancy outcomes) . Increased weight can also affect insulin levels in women, which in turn can affect fertility . Obesity can affect the hormonal signals to ovaries and testes, so could be a factor in infertility for men as well as women. There is some evidence that programs of weight loss involving exercise and careful dieting might increase the chances of pregnancy.


There are many nutritional supplements that are claimed to improve fertility, including folate (folic acid), the trace element selenium, zinc, coenzyme Q10 and vitamins B6, B12, C and E. However there is not enough evidence to prove that supplements or increasing dietary intake of any of these can improve fertility.

One trial found that combined supplementation of zinc sulfate and folate for men increased the number of normally formed sperm. More research is needed to show if zinc and/or folate supplementation results in improved fertility. There is some research on the effects on fertility of selenium and vitamins C and E. These three substances are antioxidants. Antioxidants deactivate some by-products of oxygen metabolism which damage cells in the body.

People's levels of selenium have been decreasing over the last few decades, and this has been suggested as a possible contributor to male fertility. However, selenium supplementation is controversial in infertility. Levels which are either too high or too low have been associated with lower male fertility.  A trial of three months of selenium supplementation found some benefit from selenium supplementation in subfertile men who have low selenium levels.

Vitamin E is a nutrient that might be involved in the reproductive process. Vitamin E supplementation is claimed by some to improve male infertility. A review found that there is not enough strong research on vitamin E for male infertility66. Studies have had conflicting results, and more high quality research is needed. Vitamin E supplementation appears to be safe, and smokers may be more likely to be low in vitamin E than non-smokers.

A trial of vitamin C in women found no increase in pregnancy rates from supplementation during IVF treatment. A small trial of vitamin C in men did not find any improvement in fertility.

There has been a trial of a salt-reduced diet for women during IVF, but it found no evidence that this could improve the rate of pregnancy.

Exposure to chemicals in food and the environment

Sperm production in particular has been shown to be affected by exposure to industrial chemicals. However, it is difficult to be conclusive about many of the chemicals which are claimed to affect fertility, as there are often conflicting results of research. This is further complicated by the many complex other issues of exposures and habits that can affect studies observing environmental exposure. Harm to sperm production has been linked to:


Some pesticides (dibromochloropropane - DBCP, chlordecone, ethylene dibromide and carbaryl)

Some solvents (glycol ethers, carbon disulfide, styrene and 2-bromopropane)

Some heavy metals (such as mercury and lead)


Heavy metals may also adversely affect women's fertility.

Sperm production is also adversely affected by ionising radiation and heat, and may also be affected by high-frequency electromagnetic radiation (such as in radar operators).

Vitamin C is sometimes recommended as a means of lowering the effects of heavy metals on sperm production. However, Vitamin C has not been shown to decrease levels of heavy metals in semen.

Many common plants can be used to influence fertility, including red clover, partridge berry, liferoot, wild carrot, and wild yam. Some of these grow wild, others are easy to cultivate, and, with the exception of wild carrot, all are also readily available at health food stores.

Chelation therapy did not lead to normal sperm counts, although there was some improvement. Another study (again, not a trial) found some benefit from chelation therapy for women with infertility who had been diagnosed as having excessive heavy metals in their urine.

One of the main dietary sources of chemicals and metals that might affect fertility is fish. Sea pollution has resulted in toxic levels of some chemicals in fish in many parts of the world. Fish contaminated with either mercury or PCB (polychlorinated biphenyls) have been found to contribute to lowered fertility in men and/or women in Hong Kong, India and the USA. However, a study in coastal areas in Sweden found an association between high fish consumption and infertility only among women who also smoked.

Aflatoxin is a mould that is concentrated in grains grown in drought conditions. Concentrations can get high in peanut and corn-based foods from dry areas, and the US Food and Drug Administration (FDA) monitors aflatoxin levels for safety reasons. A study in Nigeria has found that infertile men have higher than usual concentrations of aflatoxin in their semen, and that aflatoxin might be able to damage sperm. We could find no studies to show effects of avoiding certain foods to reduce possible exposure to aflatoxin.

The other dietary 'vehicle' sometimes suggested as bringing hormonal or other substances into the body, which could affect fertility, is milk (and dairy products)81. However, we could find no studies establishing such a link, or showing the effects on fertility of avoiding dairy products.

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