African-American women who have a diet high in calcium and low in lactose may have reduced risk for ovarian cancer, according to the results of a large population-based study.
The study, “Dairy, calcium, vitamin D and ovarian cancer risk in African–American women,” published in the British Journal of Cancer, also shows that those who have longer sun exposure in the summer months may have lower risk for developing the disease.
Ovarian cancer ranks fifth in cancer deaths among women and the American Cancer Society estimates that more than 14,000 women in the U.S. will die from the disease in 2016. Although the five-year survival rates improved in whites from 35% in 1975-1977 to 46% in 2005-2011, they actually worsened in African Americans, dropping from 42% to 38%. Researchers are working to identify risk factors that can be modified to improve these survival rates.
Previous studies had revealed an association between milk consumption or lactose intake with the risk of ovarian cancer, but the results were contradictive. These studies focused mainly on the European population and did not address the importance of dairy consumption in the African-American population.
Rutgers Cancer Institute of New Jersey investigators examined data from patients included in the African-American Cancer Epidemiology Study, an ongoing population-based, case-control study of ovarian cancer in African-American women in 11 U.S. states. Eligible participants were African-Americans aged 20 to 79 years who had newly diagnosed invasive epithelial ovarian cancer. These were compared with healthy self-identified African-American women selected through random-digit phone dialing.
The study included 490 women with ovarian cancer and 656 healthy controls who completed a phone questionnaire regarding a number of lifestyle factors, including how many hours they spent in the sun weekly, and how much dairy products they consumed.
Researchers found that whole milk consumption and lactose intake were significantly associated with an increase in the risk for ovarian cancer in African-American women. However, no association was found with low-fat milk or other dairy products, such as cheese or yogurt.
Calcium intake, on the other hand, reduced the risk for ovarian cancer, with those consuming higher amounts of calcium showing half the risk for ovarian cancer compared to those who consumed low levels of calcium.
Although vitamin D intake as a supplement did not affect the risk for ovarian cancer, the research team noticed that less than 20% of the women in the study consumed the recommended levels of vitamin D of at least 600 IU (or 800 IU if they were age 70 or older).
The research team also found a correlation between sun exposure, which is critical to produce vitamin D, and ovarian cancer risk. Those who spent more than 23 daylight hours a week outdoors in summer months had 30% less risk of developing the disease, compared to women who spent less than six hours a week in the sun over the summer.
This is in line with previous findings showing that while Caucasian women need only five to 15 daily minutes of sun during spring, summer and fall to have adequate amounts of vitamin D production, African-American women require five to 10 times longer because of their skin pigments.
“In addition to food and supplemental intakes, vitamin D in humans can also be produced through skin synthesis upon sun exposure. However, darker color of the skin reduces the penetration of UVB, resulting in a subsequent less cutaneous synthesis of vitamin D,” Bo Qin, PhD, and colleagues wrote.
“Because the benefits of increased sun exposure in African-American women may be offset by an increased risk of skin cancer, a combination of moderate sun exposure coupled with sufficient vitamin D intake from diet and supplements may be a safer solution for adequate vitamin D levels,” Qin, the study’s lead author said in a press release.
The researchers noted their research adds important information to the currently limited knowledge about the causes of ovarian cancer in the African-American community.
“Given that we were able to recruit a large sample of healthy African-American women and those with ovarian cancer from various geographic regions with diverse socioeconomic and lifestyle characteristics, we are able to generalize our findings to the African-American population,” said Elisa Bandera, MD, PhD, who is co-leader of the Cancer Prevention and Control Program at Rutgers Cancer Institute.
“Considering there is no effective screening tool for ovarian cancer and that African-American patients have poor survival rates with this disease, prevention through lifestyle or dietary modifications is critical,” Bandera added.