Abstract
At present, between 10 to 15% of couples are infertile, and half of all infertility cases are credited to a female factor. Determination of the source of the problem may hold the key to improving fertility for women. Emerging research demonstrates that reactive oxygen species and oxidative stress (OS) have strong connections with female reproductive function; increases in OS which is associated with certain lifestyle factors can negatively impact female fertility. Lifestyle factors including being obese or underweight, exercising, cigarette smoking, alcohol and caffeine consumption, drug use, psychological stress and environmental and occupational exposures can all have adverse effects on fertility due to their complex interactions and impact exerted via OS on female reproductive processes. Our review highlights these linkages to explain their impact on female fertility, as well as provide suggestions to reduce OS and improve reproductive potential in women.
Financial & competing interests disclosure
The authors have no relevant affliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript.
No writing assistance was utilized in the production of this manuscript.
Key issues
• A number of conditions affecting fertility in women, including endometriosis, polycystic ovary syndrome, recurrent pregnancy loss and unexplained infertility are associated with a systemic increase in reactive oxygen species (ROS) or oxidative stress (OS).
• Obesity is linked to ovarian dysfunction, compromised oocyte and embryo quality and longer times to conception. Positive correlations have been found between increasing BMI and ROS, as well as negative correlations between BMI and antioxidants.
• Being underweight can be a risk factor for infertility. Women who have eating disorders do not take enough micronutrients and therefore have lower antioxidant levels. Women who are underweight tend to have higher levels of OS markers.
• Excessive exercise can negatively impact fertility by increasing oxygen consumption, and thereby increasing the ROS released by cells. Nutritional supplements and antioxidants may be protective against exercise-induced OS.
• Impaired ovarian function and decreased oocyte and embryo quality are often associated with women who smoke cigarettes. Smoking has been associated with a decrease in serum antioxidant levels as well as increases in ROS.
• Maternal alcohol consumption is associated with a longer time to pregnancy and elevated risk for spontaneous abortion, as well as with increased levels of markers of oxidative damage.
• Women who use recreational drugs and consume caffeine are more likely to develop infertility associated with a tubal factor or an ovulatory-abnormality, and have increased risks of spontaneous abortion and still birth, respectively. The substances have been found to possess both pro-oxidant and antioxidant capabilities.
• Psychological stress may be responsible for subfertility, potentially by disrupting the production of key hormones. Although to date there is little conclusive evidence, there may be a causal link between stress and an increase in oxidative DNA damage.
• Environmental and occupational exposure to chemicals is associated with menstrual abnormalities, spontaneous abortion and pre-term delivery. Levels of polychlorinated biphenyls, pesticides and urban air pollutants are correlated with markers of OS.
• The outcomes of IVF and intracytoplasmic sperm injection procedures may also be negatively affected by the oxidative damage associated with lifestyle factors such as weight, exercise, recreational and illicit substances, stress and environmental exposures.
• Lifestyle modification should be the first course of treatment to improve fertility potential. Antioxidants and other supplements may confer additional benefits by further combating ROS. Assisted reproductive technology should be considered only if less extreme, minimally invasive methods are unsuccessful.