Student Scholarship – First Place Research Review 

DAIANA CASTLEMAN, HBSC 

STEFANIE TROWELL, ND 

Women today are increasingly aware of the impact age has on their fertility. Armed with the knowledge that female fecundity begins to decrease after age 32, and decreases even more rapidly after age 37,¹ younger women are undergoing fertility testing well before trying to conceive. For some women, this may be due to a desire to delay childbearing. Professional development, financial security, and the presence of an appropriate partner are all reasons some women may decide to wait.² For other women, they may simply wish to know if they are likely to experience problems when they do decide to conceive. Regardless, younger women are entering their doctors’ offices wanting to preserve their eggs. In order to respond to the needs of women who want to be more proactive in preserving and protecting their fertility, it is important to look beyond age. Physical activity, diet, stress, and sleep are important lifestyle factors that can all influence fertility outcomes and should be considered as part of a well-constructed fertility consultation. 

Physical Activity 

Physical activity influences reproductive hormone levels and energy balance, which in turn can impact fertility. High levels of physical activity have been associated with increased menstrual cycle length,³ increased follicular phase length,⁴ and decreased luteal phase length,^5,6 all of which represent hormonal changes and can reduce the window for implantation. A Danish study of 3628 women found that vigorous physical activity (>5 hours per week) was associated with decreased fecundability.⁶ In another study, based on population data gathered in Norway, women who exercised daily (or on most days) were more than 3 times as likely to experience difficulty conceiving than those that were less active.⁷ Additionally, women who exercised to exhaustion were more than twice as likely to experience fertility problems.⁷ In contrast, moderate exercise (16-60 minutes) was associated with a decreased risk of infertility when compared to the shortest duration of exercise (<15 minutes) in the same study.⁷ Moderate exercise has also been associated with improved Assisted Reproductive Therapy (ART) outcomes,⁸ and for women undergoing intracytoplasmic sperm injection (ICSI), regular exercise (3 times per week, regardless of duration, modality, or intensity) improved implantation and pregnancy rates and reduced the risk of miscarriage.⁹ 

Interestingly, the impact of physical activity on fertility may vary depending on body mass index (BMI). The Danish study found that moderate exercise was associated with increased fecundability in all BMI ranges, but vigorous exercise did not negatively affect fecundability in women with a BMI of over 25 kg/m².⁶ Another way to consider the impact of BMI on fertility is in terms of the length of time actively trying to conceive until pregnancy. Time to conception increases in women with low and high BMIs. Underweight women (<19 kg/m²) have a fourfold longer time to pregnancy than women who have a healthy BMI (19-24 kg/m²).¹⁰ Women who have a BMI greater than 25 kg/m² have a twofold longer time to pregnancy.¹⁰ These changes in time until conception are likely due to the fact that BMI is indicative of energy balance, and in terms of preserving their fertility, women with different BMIs may benefit from different physical activity regimens. 

Diet 

Optimizing diet continues to be a cornerstone of preconception care, and evidence suggests more frequent intake of healthier food reduces time to pregnancy.^11–13 A 2020 literature review found evidence that increasing intake of fruit (3 servings per day), avoiding fast food and sugary beverages, and eating a diet of lower glycemic index foods, have been associated with less time to pregnancy.¹¹ The Mediterranean-type dietary pattern was similarly associated with reduced difficulty conceiving when compared to a Western-type diet.¹² In the United Kingdom, pregnant women are advised to eat 5 servings of fruits and vegetables per day, limit caffeine to 300 mg per day, and to abstain from tobacco or alcohol.¹⁴ A longitudinal study, conducted in Southampton, UK, found that 47% of women did not achieve the minimum recommendation for daily fruit and vegetable intake.¹⁴ This finding highlights the fact that, despite focused interventions designed to improve the diets of pregnant women, there is room for improvement in helping women achieve the balance of dietary macronutrients to best support reproductive health.  

Carbohydrate 

Observational studies suggest that the consumption of whole grains, vegetables, and fruit positively influence female fertility.^13,15 These carbohydrate sources have been associated with higher embryo quality at the cleavage stage, with fruit consumption specifically associated with a greater likelihood of blastocyst formation.¹⁵ In the Nurses’ Health Study II (NHS II), a large-cohort longitudinal study that began in 1989, diets with a low glycemic load were associated with a 66% lower risk of ovulatory disorders and a 27% lower risk of other causes of infertility.¹³ In the same study, high glycemic index foods such as cold breakfast cereals, white rice, and potatoes, were associated with a greater risk of ovulatory infertility.¹⁶ The data collected from the NHS II study also revealed that even in otherwise healthy, reproductive-aged women, altering the type of carbohydrate and its subsequent impact on blood sugars can improve fertility outcomes.¹⁶ 

Fat 

Low omega-3 and high trans-fatty acid intake have been associated with reduced fecundity.¹⁷ In a 2018 prospective cohort study of 351 women who underwent infertility treatment, increasing fish intake was associated with a 34–48% higher probability of live birth (as opposed to poultry, red meat, or processed meat).¹⁸ In the same study, replacing other types of meat with 2 servings of fish per week increased the likelihood of a live birth by 54-64%.¹⁸ These results are consistent with other research, including the NHS II data, which found that limiting saturated and trans fats – while consuming a diet high in omega-3 and monounsaturated fats – were associated with positive impacts on fertility.^19,20  

Protein 

In a study of 269 women undergoing ICSI, consuming red meat was associated with a negative influence blastocyst formation.¹⁵ Replacing animal sources with vegetable sources of protein, however, may reduce ovulatory infertility risk.^21,13 A prospective analysis of the NHS II data estimated that women who consumed 5% of their daily energy intake as plant-based protein, rather than animal based, could reduce their risk of ovulatory infertility by more than 50%.²¹ Questions have also been raised about the potential for protein sources from animals to contain environmental contaminants, such as hormonal residues, mercury, and other endocrine-disrupting chemicals. Women can avoid these questions by attempting to learn as much as possible about the origins of their protein sources before purchasing them. 

Caffeine 

There does not appear to be any association between caffeine consumption and fecundity.²² However, caffeine consumption above 300 mg per day has been associated with an increased risk of spontaneous abortion,²² which women may wish to take into consideration when it comes time to conceive. 

Alcohol 

Alcohol is a reproductive toxin which can impact multiple reproductive parameters, and it may be best for women thinking about conception to avoid alcohol entirely. For example, the likelihood of blastocyst formation and the quality of day-3 embryos has been negatively correlated with the consumption of alcoholic beverages.¹⁵ In 2003 Danish study, which analyzed data collected from more than 11 000 women between 1991 and 1993, it was found that women over the age of 30 who consumed 1-6 drinks per week exhibited an increased risk of infertility when compared to women that consumed less than 1 drink per week. ²³ In a similar study, women who abstained from alcohol entirely had an increased rate of conception when compared to women that consumed 1-5 drinks per week.²⁴ In a 2017 review that examined the potential for creating a “safe dose” for alcohol, the authors concluded that women who are pregnant or attempting to conceive “should be advised against consuming any amount of alcohol,” and that women attempting to conceive should not be allowed to participate in ART therapy if they cannot severely limit or otherwise abstain from alcohol entirely.²⁵  

Stress 

The magnitude of impact stress has on female fertility remains uncertain. It is well documented, however, that stress can lead to a myriad of reproductively detrimental effects, such as sleep disturbances, depressive symptoms, uptake of unhealthy behaviors (eg, consumption of tobacco, alcohol, and caffeine), lower intercourse frequency, and abnormal menstruation.²⁶ Smoking, an inferior coping strategy reproductively speaking, is specifically associated with shorter menstrual cycles (<24 days).²⁷ In a meta-analysis that compared smoking with non-smoking women, researchers found that smoking women were 1.6 times more likely to experience infertility.²⁸ In addition, women undergoing ART who reported more marital stress required significantly more treatment cycles to conceive than women reporting less marital stress.²⁹ 

A 2018 study of women aged 21-45 also found that greater perceived stress scores among women (Perceived Stress Scale score ≥20) were associated with reduced fecundability.²⁶ These findings were amplified for women attempting conception for 0-2 menstrual cycles versus 3-6 cycles at enrollment.²⁶ Another study assessed the impact of stress on fecundability by measuring salivary cortisol and alpha-amylase levels (indicators of sympathetic tone).³⁰ Interestingly, women in the study had a similar time to pregnancy until around 5 menstrual cycles. At that time, women who had alpha-amylase levels in the highest third began to demonstrate lower probabilities of pregnancy.³⁰ Women with the highest third of alpha-amylase levels had a twofold increased risk of infertility compared to women in the lowest third.³⁰ There were no significant associations observed between the likelihood of pregnancy and salivary cortisol levels.³⁰ In a similar study, stress (also measured using salivary alpha-amylase concentrations) was shown to reduce the probability of conception irrespective of the day or frequency of sexual intercourse during the fertile window.³¹ 

Stress may also impact anti-müllerian hormone (AMH), a marker of ovarian reserve. Chronic psychosocial stressors, such as a personal history of abuse or recreational drug use, have been associated with a fourfold increased risk of diminished ovarian reserve.³² Despite this correlation, current research does not support AMH as a predictor of fertility in general, and further studies are needed to clarify the relationship between stress, ovarian reserve, and fertility outcomes.^33,34  

Sleep 

Disrupted sleep patterns have been associated with hormonal imbalances and poor reproductive outcomes for women. In a 2014 meta-analysis, researchers found that women performing shift work (work outside 8:00 AM to 6:00 PM), when compared to women who worked regular hours, exhibited a 33% higher rate of menstrual disruption and an 80% higher rate of subfertility.³⁵ In addition, women with more variable sleep schedules have been shown to have higher circulating levels of estradiol.³⁶ Elevated estradiol can suppress follicle-stimulating hormone (FSH), which can impair conception.  

Total sleep duration is also an important consideration for female fertility. Sleeping less than 6 hours per night has been associated with a drop of up to 20% in circulating FSH levels.³⁷ Sleeping less than 8 hours per night has also been identified as a potential risk factor for miscarriage in the first trimester.³⁸ In a study of 50 154 women with non-apnea sleep disorders, the risk of developing infertility was 3.7 times higher in women with disordered sleep patterns, when compared to women who slept longer and more regularly.³⁹ Both the quality and quantity of sleep, likely through their influence on reproductive hormones, appear to have clinically significant impacts on fecundity. 

Summary 

Though age is often considered a primary determinant of women’s reproductive health, diet and lifestyle factors are important considerations that can impact fertility. Based on the available research, women who are interested in taking additional steps toward maintaining their reproductive health can focus their efforts on the following interventions: 

• Engage in healthy weight management 
• Complete moderate to vigorous activity for 16-60 minutes per day, 3-5 days per week 
• Eat a diet that prioritizes fruits and vegetables 
• Avoid high glycemic index foods 
• Include fish and plant-based sources of protein 
• Avoid potential environmental contaminants 
• Limit caffeine intake 
• Consider abstaining from, or severely limiting, any alcohol consumption 
• Include stress management and healthy coping techniques 
• Avoid using alcohol, tobacco, or caffeine to help mitigate stress 
• Prioritize regular sleep of at least 8 hours per night 

The millennial generation may be the most proactive generation in history in terms of mitigating potential difficulties with conception. It is up to us as practitioners to not only inform them about how to preserve and protect their fertility, but to also help educate and empower them throughout the process. 

References

1. American College of Obstetricians and Gynecologists Committee on Gynecologic Practice and Practice Committee. Female age-related fertility decline. Committee Opinion No. 589. Fertil Steril. 2014;101(3):633-634.  

2. Maheshwari A, Porter M, Shetty A, Bhattacharya S. Women’s awareness and perceptions of delay in childbearing. Fertil Steril. 2008;90(4):1036-1042. 

3. Cooper GS, Sandler DP, Whelan EA, Smith KR. Association of physical and behavioral characteristics with menstrual cycle patterns in women age 29-31 years. Epidemiology. 1996;7(6):624-628. 

4. Liu Y, Gold EB, Lasley BL, Johnson WO. Factors affecting menstrual cycle characteristics. Am J Epidemiol. 2004;160(2):131-140. 

5. De Souza MJ, Miller BE, Loucks AB, et al. High frequency of luteal phase deficiency and anovulation in recreational women runners: blunted elevation in follicle-stimulating hormone observed during luteal-follicular transition. J Clin Endocrinol Metab. 1998;83(12):4220-4232. 

6. Wise LA, Rothman KJ, Mikkelsen EM, et al. A prospective cohort study of physical activity and time to pregnancy. Fertil Steril. 2012;97(5):1136-1142. 

7. Gudmundsdottir SL, Flanders WD, Augestad LB. Physical activity and fertility in women: the North-Trøndelag Health Study. Hum Reprod. 2009;24(12):3196-3204. 

8. Harrison CL, Brown WJ, Hayman M, Moran LJ, Redman LM. The Role of Physical Activity in Preconception, Pregnancy and Postpartum Health. Semin Reprod Med. 2016;34(2):e28-e37. 

9. Ferreira RC, Halpern G, de Cássia Savio Figueira R, et al. Physical activity, obesity and eating habits can influence assisted reproduction outcomes. Womens Health (Lond). 2010;6(4):517-524. 

10. Hassan MA, Killick SR. Negative lifestyle is associated with a significant reduction in fecundity. Fertil Steril. 2004;81(2):384-392. 

11. Grieger JA. Preconception diet, fertility, and later health in pregnancy. Curr Opin Obstet Gynecol. 2020;32(3):227-232. 

12. Toledo E, Lopez-del Burgo C, Ruiz-Zambrana A, et al. Dietary patterns and difficulty conceiving: a nested case-control study. Fertil Steril. 2011;96(5):1149-1153. 

13. Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Diet and lifestyle in the prevention of ovulatory disorder infertility. Obstet Gynecol. 2007;110(5):1050-1058. 

14. Crozier SR, Robinson SM, Borland SE, et al. Do women change their health behaviours in pregnancy? Findings from the Southampton Women’s Survey. Paediatr Perinat Epidemiol. 2009;23(5):446-453. 

15. Braga DP, Halpern G, Setti AS, et al. The impact of food intake and social habits on embryo quality and the likelihood of blastocyst formation. Reprod Biomed Online. 2015;31(1):30-38. 

16. Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. A prospective study of dietary carbohydrate quantity and quality in relation to risk of ovulatory infertility. Eur J Clin Nutr. 2009;63(1):78-86. 

17. Wise LA, Wesselink AK, Tucker KL, et al. Dietary Fat Intake and Fecundability in 2 Preconception Cohort Studies. Am J Epidemiol. 2018;187(1):60-74. 

18. Nassan FL, Chiu YH, Vanegas JC, et al. Intake of protein-rich foods in relation to outcomes of infertility treatment with assisted reproductive technologies. Am J Clin Nutr. 2018;108(5):1104-1112. 

19. Silvestris E, Lovero D, Palmirotta R. Nutrition and Female Fertility: An Interdependent Correlation. Front Endocrinol (Lausanne). 2019;10:346. 

20. Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Dietary fatty acid intakes and the risk of ovulatory infertility. Am J Clin Nutr. 2007;85(1):231-237. 

21. Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Protein intake and ovulatory infertility. Am J Obstet Gynecol. 2008;198(2):210.e1-210.e2107. 

22. Lyngsø J, Ramlau-Hansen CH, Bay B, et al. Association between coffee or caffeine consumption and fecundity and fertility: a systematic review and dose-response meta-analysis. Clin Epidemiol. 2017;9:699-719. 

23. Tolstrup JS, Kjaer SK, Holst C, et al. Alcohol use as predictor for infertility in a representative population of Danish women. Acta Obstet Gynecol Scand. 2003;82(8):744-749. 

24. Jensen TK, Hjollund NH, Henriksen TB, et al. Does moderate alcohol consumption affect fertility? Follow up study among couples planning first pregnancy. BMJ. 1998;317(7157):505-510. 

25. Van Heertum K, Rossi B. Alcohol and fertility: how much is too much?. Fertil Res Pract. 2017;3:10. 

26. Wesselink AK, Hatch EE, Rothman KJ, et al. Perceived Stress and Fecundability: A Preconception Cohort Study of North American Couples. Am J Epidemiol. 2018;187(12):2662-2671. 

27. Rowland AS, Baird DD, Long S, et al. Influence of medical conditions and lifestyle factors on the menstrual cycle. Epidemiology. 2002;13(6):668-674. 

28. Augood C, Duckitt K, Templeton AA. Smoking and female infertility: a systematic review and meta-analysis. Hum Reprod. 1998;13(6):1532-1539. 

29. Boivin J, Schmidt L. Infertility-related stress in men and women predicts treatment outcome 1 year later. Fertil Steril. 2005;83(6):1745-1752. 

30. Lynch CD, Sundaram R, Maisog JM, et al. Preconception stress increases the risk of infertility: results from a couple-based prospective cohort study–the LIFE study. Hum Reprod. 2014;29(5):1067-1075. 

31. Louis GM, Lum KJ, Sundaram R, et al. Stress reduces conception probabilities across the fertile window: evidence in support of relaxation. Fertil Steril. 2011;95(7):2184-2189. 

32. Pal L, Bevilacqua K, Santoro NF. Chronic psychosocial stressors are detrimental to ovarian reserve: a study of infertile women. J Psychosom Obstet Gynaecol. 2010;31(3):130-139. 

33. Hawkins Bressler L, Steiner A. Anti-Müllerian hormone as a predictor of reproductive potential. Curr Opin Endocrinol Diabetes Obes. 2018;25(6):385-390. 

34. Dewailly D, Laven J. AMH as the primary marker for fertility. Eur J Endocrinol. 2019;181(6):D45-D51. 

35. Stocker LJ, Macklon NS, Cheong YC, Bewley SJ. Influence of shift work on early reproductive outcomes: a systematic review and meta-analysis. Obstet Gynecol. 2014;124(1):99-110. 

36. Merklinger-Gruchala A, Ellison PT, Lipson SF, et al. Low estradiol levels in women of reproductive age having low sleep variation. Eur J Cancer Prev. 2008;17(5):467-472. 

37. Touzet S, Rabilloud M, Boehringer H, et al. Relationship between sleep and secretion of gonadotropin and ovarian hormones in women with normal cycles. Fertil Steril. 2002;77(4):738-744. 

38. Samaraweera Y, Abeysena C. Maternal sleep deprivation, sedentary lifestyle and cooking smoke: Risk factors for miscarriage: A case control study. Aust N Z J Obstet Gynaecol. 2010;50(4):352-357. 

39. Wang ID, Liu YL, Peng CK, et al. Non-Apnea Sleep Disorder Increases the Risk of Subsequent Female Infertility-A Nationwide Population-Based Cohort Study. Sleep. 2018;41(1):10.1093/sleep/zsx186. 

Daiana Castleman, HBSc is a 4^th year student at the Canadian College of Naturopathic Medicine. She completed her undergraduate degree at McMaster University, double majoring in Biology and Psychology. Prior to starting her naturopathic program, she worked as a research assistant at St. Joseph’s Hospital in Hamilton, Ontario, in the Department of Psychiatry and Behavioural Neurosciences. She has a passion for educating women, counseling them on their fertility options, and optimizing their health so that they can meet their fertility goals. She also helps women go from feeling “burnt out” to “calm and energized,” so that every day, they can show up as their best self. 

Stefanie Trowell, ND, helps women and their partners optimize their health to achieve their fertility and wellness goals at her private practice, Insight Naturopathic, in Toronto, Ontario. She is passionate about finding the right balance of supportive care and education throughout preconception, pregnancy, postpartum, and early childhood. Dr Trowell is also a lecturer and clinical supervisor at the Canadian College of Naturopathic Medicine. Previously, she worked on innovative research in neuroscience, endocrinology and reproduction. She now focuses her problem-solving skills on understanding the complexities of hormonal balance and mitochondrial health – key components of both reproductive and physical health.