June 2013

Self-Report of Fruit and Vegetable Intake that Meets the 5 a Day Recommendation Is Associated with Reduced Levels of Oxidative Stress Biomarkers and Increased Levels of Antioxidant Defense in Premenopausal Women

Oxidative stress is a condition in which an overproduction of free radicals and reactive oxygen species cause damage to components of the body- DNA, lipids, and proteins in particular.   In addition to many chronic diseases, oxidative stress has been associated with several reproductive disorders including infertility, impaired follicular growth, endometriosis, spontaneous abortion, and increased risk for delivering a low-birth-weight infant.  Because of these risks, it is important to understand the potential mediators of oxidative stress for women of reproductive age.

Fruits and vegetables are among the best sources of antioxidants- a substance that may protect cells from oxidative stress.  Antioxidants include vitamins C and E, carotenoids, flavanoids, and numerous other phytochemicals.  Recent campaigns to increase fruit and vegetable intake aim to increase consumption in hopes of reducing the risk of chronic disease while providing low-calorie food choices for maintaining a healthy weight.  One such campaign recommended by the National Cancer Institute is the “5 A Day For Better Health” campaign.  The suggestion of this particular campaign is for Americans to consume 5 servings of any combination of fruits and vegetables a day, however only 59% of Americans are meeting the recommendations for vegetables and 42% for fruit. 

The effect of diets rich in fruits and vegetables on oxidative stress remains controversial.  Some studies show that there are decreased levels of oxidative stress markers among those who consume a fruit and vegetable rich diet, while other studies show no such association.  Additionally, studies exploring the supplementation of purified antioxidants have shown no protection against chronic disease and even increased risk of disease in some rare cases. 

Previous studies have shown that oxidative stress levels can vary across the different phases of the menstrual cycle.  Because of reproductive implications, this study aimed to fill important data gaps by exploring the relationship between oxidative stress and F/V consumption while taking menstrual cycle variability into account. 

Participants in this study included 258 healthy, regularly menstruating women between 18 and 44.  Exclusion criteria included: current use of oral contraceptives or use during the past 3 months, regular intake of a vitamin and mineral supplement, current prescription medications, and a body mass index of <18 or >35.

Participants were followed for up to two menstrual cycles, with up to eight visits to the clinic per cycles.  Dietary intake was assessed through both food frequency questionnaires and 24-hour recalls.  FFQ was administered three times, once at baseline and then at the end of each cycle.  24-hour recalls were conducted up to four times per cycle.  Biological specimens were collected in a number of ways.  Fasting blood samples were collected at each cycle visit.  Lipid peroxidation measurements were performed using ethylenediaminetetraacetic acid anticoagulated blood plasma.  Fat-soluble antioxidant vitamins were measured by high-performance liquid chromatography.  Antioxidant enzymes were measured using kinetic enzyme assays.

Statistical analysis included both descriptive statistics and multivariable models.  The descriptives compared women who did and did not meet the recommendation by calculating means levels of lipid peroxidation, antioxidant enzymes, and antioxidant vitamins by menstrual cycle phase.  Multivariable models were used to determine the correlation between oxidative stress and antioxidant measures between and within participants who did and did not meet the 5 a day recommendation.  The final models were adjusted for age, energy intake, race, income, marital status, parity, and former oral contraceptive use.

The results of this study showed that the majority of the women in this cohort did not meet the 5 a day recommendation for F/V.  Those who did meet the recommendation tended to be older, white, married with children, and have higher income.   Meeting the 5 a day recommendation was associated with greater energy intake, however no differences were noted for BMI, physical activity, education, and smoking.

F2-isoprostanes, a marker of lipid oxidation was observed to be significantly lower across the menstrual cycle for women who consumed five servings of F/V each day.  Additionally, super oxide dismutase, an antioxidant enzyme, was lower among those who met the recommendation.  Most antioxidant vitamins were significantly higher when five servings of F/V per day were met.  Multivariable analyses revealed that results were consistent for both cycle phase-specific models and typical diet analysis. 

In conclusion, among healthy premenopausal women, this study found that meeting the 5 A Day For Better Health Program recommendations were associated with lower levels of lipid peroxidation, lower concentration of erythrocyte antioxidant enzymes, and higher concentration of most plasma/serum antioxidant vitamins.