Study: Diet during teen years and early adulthood is linked to breast cancer risk

IN-DEPTH REVIEW OF RESEARCH

Study background:

Although the effect of adult diet on cancer risk has been well studied, statistical models and animal studies suggest that the years before a woman has her first child are critical when trying to estimate breast cancer risk. This study specifically looks at how a woman’s diet during her teenage years and early adulthood affects breast cancer risk.  

Researchers of this study wanted to know:

How a woman’s diet during her teenage years and young adulthood affects her risk of breast cancer later in life.

Population(s) looked at in the study:

Holly R. Harris and colleagues used data from the Nurses’ Health Study, which began in 1989. At the beginning of the study 116,430 nurses participated by filling out a questionnaire on their lifestyle and medical history. Eight years later, 47,355 participants (who were 33 to 52 years old the time) completed a second questionnaire about their diet during high school. Women were excluded from the analysis if their reported daily caloric intake was less than 500 calories or greater than 5,000 calories, if they left more than 20 questions unanswered, if they did not report their height, or if they were diagnosed with any cancer except melanoma.

Adolescent diet was measured by asking the participants which of 124 food items they ate, including foods that were commonly eaten from 1960 to 1980 when they would have been in high school. These women first reported their adult diets in 1991, when they were 27 to 44 years old. That survey included 130 food items and was completed every 4 years. For both adolescent and adult surveys, participants were asked how often, on average, they had eaten each food item, ranging from “never” to “6 or more times a day.”  

Every other year, participants were asked if they had been diagnosed with breast cancer in the previous 2 years.  They were considered premenopausal if they still had periods, or had at least one ovary remaining if they were 48 years old or older.  Women were considered postmenopausal if they reported being so due to natural menopause or bilateral oophorectomy.  

The inflammatory diet pattern was previously identified in other studies; researchers looked at the levels of biomarkers of inflammation (certain molecules know to be elevated during an inflammatory response) in participants blood.  They then compared biomarker levels to the food items the participants ate.

Researchers in this study analyzed diets and breast cancer in three categories: adolescent (ages 13 to18), early adulthood (ages 27 to 44), and combined diets (adolescent and early adulthood).  They also looked at other variables.  Adolescent variables included age, total adolescent calories, height at age 18, age at which their periods began, body mass index, and adolescent physical activity.  These same variables were included for adult women. Premenopausal women were also asked about age at first childbirth, number of children delivered, oral contraceptive use, adult physical activity, alcohol consumption, weight change since age 18, and history of benign breast disease. Postmenopausal adult variables included age at menopause and hormone usage.    

Study findings: 

Among the 45,204 study participants, 1,477 cases of breast cancer were reported over the 22-year follow-up: 870 premenopausal cases and 490 postmenopausal cases.

• Women who consumed an inflammatory diet during adolescence: 
  • had a higher Body Mass Index (BMI) at age 18
  • were less physically active in adulthood
  • gained more weight since age 18
  • were more likely to have used oral contraceptives 
  • ate an average 3.3 servings of refined grains and 1.2 servings of red meat a day
• Women whose diet was low in inflammatory foods: 
  • ate 1.5 servings of refined grains and 0.6 servings of red meat a day
  • on average, these women also ate 0.7 servings a day of leafy vegetables compared to 0.3 servings for women whose diet pattern included inflammatory food

The most significant finding was:

• Women who remembered having eaten a very highly inflammatory diet as teens were 35% more likely to develop premenopausal breast cancer than women who ate the least inflammatory diet.
• Women who remembered having eaten a very highly inflammatory diet as young adults were 40% more likely to develop premenopausal breast cancer than women who ate the least inflammatory diet.

Among all participants, an adolescent inflammatory diet was associated with premenopausal breast cancer, and among all foods eaten, adolescent intake of processed meats was the food type most strongly associated with this risk. No association was made with an adolescent inflammatory diet and overall or postmenopausal breast cancer.

Limitations:

Few studies on adolescent diet and breast cancer have been conducted because of the difficulty in accurately reporting diet during this time. To accurately collect this data researchers would have to randomly assign large numbers of teenagers to eat different diets and then follow them for over 20 years. Among the few studies reported, eating higher amounts of soy and fiber during adolescence has been linked to reduced breast cancer risk, while eating red meat during adolescence has been shown to increase the risk of premenopausal breast cancer. More research is needed to confirm the results presented in this study.

Researchers did have not have participants’ adolescent biomarker levels. If foods eaten during adolescence influence biomarkers levels differently than they do in adults, this would not be detected in this study. Other limitations were that participants self-reported dietary information, and they were 33 to 52 years old when they were asked to remember their diets decades before, during high school. While recalling one’s adolescent diet has been shown to be reasonable, some reporting error is likely. It is also possible that teens who ate more nutritiously during adolescence had other lifelong healthy habits which were not taken into account.

Conclusions:

In summary, this new report suggests that women who ate an inflammatory diet during adolescence and early adulthood were at increased risk of premenopausal breast cancer. The results of this study are important because very little is known about how adolescent diet contributes to risk of premenopausal breast cancer. Eating less refined flour, sugar, and red meat and eating more vegetables provides many healthful benefits, and this study shows that doing so early in life can impact the risk of premenopausal breast cancer. “A healthy lifestyle early on is much, much more important than we appreciated,” Michels said. “Now we have to communicate this to girls.”   

Posted 6/30/17