Association of Mammographic Breast Density with Dairy Product Consumption, Sun Exposure, and Daily Activity

Background. Mammographic density is a risk factor, for breast cancer and its association with various factors is under investigation; we carried out a study to assess its relationship with daily dairy intake, sun exposure, and physical activities. Patients and Methods. Women ≥40 years of age were interviewed about habits of dairy product consumption, daily sun exposure and physical activity. Exclusion criteria consisted of history of breast cancer, consumption of calcium and vitamin D supplements, hormone replacement therapy, or renal disease. Mammographic densities were classified according to the classification system of the American College of Radiologists into 4 classes. Results. Overall 703 cases were entered in the study. The mean age was 48.2 ± 6.2 years. The most common and least frequent classes of mammographic density were classes 2 and 4, respectively. There was no significant association between mammographic density and rate of dairy consumption, amount of sunlight exposure, and daily physical activity. Conclusion. Relation of sunlight exposure and intake of milk products with mammographic density need further study, while the subject of physical activity can be evaluated by a systematic review and meta-analysis of the existing literature.


Introduction
Density of breast parenchyma in mammography is presently a feature recognized as one of the risk factors for breast cancer [1][2][3]. Relative risk for breast cancer in high density mammograms is 2-to 6-fold higher than in low density ones [1,2,4].
We conducted a study to determine the association of mammographic breast density with habits of dairy intake, daily sun exposure, and rate of daily activities.

Methods
This is a cross-sectional study completed as component of a large study being carried out in the Breast Clinic of Arash Women's Hospital, Tehran, Iran. Women aged 40 years or above who were candidates for breast cancer screening were entered in the study and those who were practicing sports or had a personal history of breast cancer, recent consumption of calcium supplements, vitamin D, or hormone replacement therapy (HRT), or any kind of renal disease were excluded. A questionnaire about habitual daily sun exposure, patterns of consumption of dairy products, and amount of daily activity of participants was filled out by a trained interviewer. Following clinical breast examination, all of them underwent screening mammography by standard bilateral mediolateral-oblique and craniocaudal views. Two expert radiologists classified the density of mammograms according  to the Breast Imaging-Reporting and Data System (BIRAD) of parenchymal mammographic classification system of the American College of Radiologists (ACR) into class 1: almost entirely fatty (<25% glandular), class 2: scattered fibroglandular densities (approximately 25-50% glandular), class 3: heterogeneously dense (approximately 51-75% glandular), and class 4: extremely dense [8,20]. Daily dairy product consumption was identified as number of servings per day. Due to the lack of a defined foodcomposition table for Iran [21], equivalent amounts of milk products making one serving were described in agreement with Canada and the United States' food guide [22,23] as well as habitual Iranian dietary patterns of eating. Each serving was assumed equal to one glass (250 cc) of milk, 40-50 grams of cheese (the size of one box of matches in Iranian cheese products), one cup (175-200 cc) of yogurt, one glass of doogh (Iranian yogurt drink composed of yogurt and water with the same consistency as milk in terms of constituents and proportions), or one glass of ice cream [24,25]. Rate of daily consumption was classified as less than one, 1 to 3, or more than 3 servings per day.
The lifestyle of most urban Iranian women is such that they stay indoors through a great proportion of the day. Therefore, we classified the time of sun exposure to less or more than half an hour in daylight each day.
Women in Iran are rather active in house work, and the small proportion which are employed or have a business outdoors accomplish their household duties to the same extent as housewives. Accordingly, daily activity was classified as mild, moderate, or severe as follows. Mild activity constituted of only house work in a small or moderate-size house or house work with help and support from others in a large house. Moderate activity was defined as house work with the same description of the mild group in addition to outdoors work or nonsupported house work in a large house. Severe activity was depicted as any amount of work more than the above.
Association between MD and the three investigated parameters was analyzed by SPSS version 16. For statistical significance, 2 test was used and < 0.05 was regarded as statistically significant. The study was approved by the Ethics Institutional Review Board of Tehran University of Medical Sciences.

Results
After excluding 135 of the participants according to the exclusion criteria, 703 cases were entered in the study. The mean age was 48.2 ± 6.2 years. Table 1 demonstrates the frequency of different classes of MD in each category of investigated variables.
Among all classes of MD, the most frequent in all participants and in each studied group was class 2 and the second most common was class 3. As well, in all groups, the least frequently detected MD was class 4, except for those who consumed more than 3 servings per day of milk products; class 1 MD was the least frequent in this group. Moreover, the only participants with a high gap between class 4 and 1 were women with mild daily physical activity.
Analysis showed no significant association between MD and milk product intake whether the participants consumed less than one, one to 3, or more than 3 servings of the products per day ( = 0.632). Likewise, the distribution of classes of MD was comparable in low and high amounts of exposure to sunlight and the difference was nonsignificant in the two groups ( = 0.283). Mild, moderate, or high levels of daily  None * * * * * * * Pub yr: Publication year, * * primarily dairy products, * * * except for a cross-sectional inverse association at age 53 years in post-menopausal women, * * * * They showed that sunlight exposure in childhood is more effective, * * * * * MD slightly higher when 3.5 hr physical inactivity per day, * * * * * * probable inverse association in overweight women.
physical activities also did not have any statistically significant effect on MD ( = 0.304).

Discussion
The high likelihood of getting involved with breast cancer in women with dense mammograms [26] has motivated the completion of numerous researches regarding factors contributing to higher densities in the breast image. Association of MD and eating patterns has been the subject of several researches. In 1999, Knight et al. investigated the effects of ingested fat on the risk of breast cancer by assessing changes of MD after 2 years of consuming low-fat, high-carbohydrate foods. They detected a significant amount of reduction in MD after the regimen; this effect was magnified in those going through menopause in that period of time [27]. Qureshi et al. roughly confirmed these results in their study but showed no relationship between MD and ingestion of foods containing vitamins and calcium or levels of protein and carbohydrate intake [28]. Nevertheless this was not validated by Sala et al. who had previously observed increased MD in women eating more protein and carbohydrate and no association of MD with fat and vitamin intake [29]. Soy-containing foods have also been recognized as probably influencing MD [12,30]. Among studies investigating the subject of food and MD, few have considered the relationship between MD and the rate of milk and milk products consumption; so far the issue is left unsolved although the bulk of existing literature might be mildly in favor of an inverse association. Some of the relevant studies are summarized in Table 2. The highest proportion of our study population either used low or moderate amounts of dairy products and only about 10% consumed an acceptable or high level of this group of nutrients. Nevertheless, nearly half of the latter group had class 2 MD, while less than onethird had class 3 and only about 10% proved to have very dense breasts on mammogram. These figures approximate those of the 2 other groups, establishing the lack of association between the two variables.
The relation of vitamin D levels and MD has been considered in several works; nevertheless the effect of sunlight exposure has rarely been investigated because of the complexity of its quantitative and qualitative estimation, and the results have been controversial (Table 2). In our study, MD did not differ significantly between the low-and highsun-exposed groups. However, although Tehran is located at 35 ∘ latitude, has a temperate climate [44], and benefits from good sunlight, the majority of female residents in Tehran live indoors for the best part of the day. Consequently, even though our classification consisted of a minimum of 30 minutes per day as the threshold for high sun-exposure, less than one quartile of the study population were categorized in this group. The lack of association of MD with this parameter may be due to the low rate of exposure even in the latter group.
Physical activity is defined as any energy spending movement of the bodyand is composed of different everyday activities as recreational, occupational, or household activity [45]. This term is not the equivalent of exercise, described as a structured and rhythmic activity performed with the purpose of achieving physical fitness. The link connecting physical activity with MD has been investigated in some studies as demonstrated in Table 2, and the majority could not come ISRN Oncology 5 across any significant association. Although the quantity of physical activity was largely different among the 3 groups in our study, it did not influence MD, confirming previous studies.

Conclusion
Our study shows no association between mammographic density and rate of dairy consumption, amount of sunlight exposure, and daily physical activity. We believe that the last issue deserves to be investigated by systematic review and meta-analysis of the existing data in the literature. Sunlight exposure and intake of calcium-containing food in regards to MD needs to be further studied.