Unraveling breast cancer connections. With breast cancer rates continuing to rise, especially among younger women, identifying those factors that elevate a woman’s risk for the disease is an ongoing concern. A major area of inquiry is reproductive factors, stemming from a 17th-century observation that breast cancer was prevalent among nuns. A 1970 study established that a full-term pregnancy early in a woman’s childbearing years reduces the risk of breast cancer. Other studies have documented possible benefits from breastfeeding, and indicated that earlier onset of regular menstrual cycles and later age at menopause may be associated with higher risk.

The role of abortion — both spontaneous (miscarriage) and induced (voluntary) — has been widely studied. Although most of the evidence indicates no association between abortion and breast cancer, controversy about it continues. For the most part, previous studies were retrospective, based on data collected only after breast cancer had been diagnosed. A recent prospective study conducted by School of Medicine Professor Julie Palmer and colleagues at the Slone Epidemiology Center found no connection between induced abortion and risk of breast cancer in African-American women.

The researchers followed women enrolled in the Black Women’s Health Study, which has been tracking the health of 59,000 African-American women since 1995. The women who did not have breast cancer at the 1995 baseline assessment were surveyed in 1997 and 1999. The current study is based on data from the 349 women reporting a first occurrence of breast cancer on one of the follow-up questionnaires. Among this group of women who had developed breast cancer, the researchers separated women who had never had children from those who had had at least one full-term pregnancy. Within each group they compared women who had had no abortions to those who had had one or more abortions. They controlled for such factors as family history of breast cancer in a first-degree relative, age at the beginning of menstruation, duration of oral contraceptive use, years of education, body mass index at baseline, age at first birth, and number of births.

Among this population of African-American women, the researchers found no evidence of an association between induced abortion and risk of breast cancer, as well as no association between miscarriage and increased risk of breast cancer. They also found no evidence of higher risk for women who had had an abortion before the age of 20; neither did abortion increase the risk among those women with an already high risk because of family history.

This study was published in Cancer Causes and Control, Volume 15, 2004.

Between a rock and a hot place. One method earth scientists use to try to understand conditions that prevailed on Earth millions of years ago is analyzing sediments deposited beneath the oceans. Recently a research team led by Andrew Kurtz, a College of Arts and Sciences assistant professor of earth sciences, examined records of carbon and sulfur isotopes in sediments buried during the early Cenozoic era. The researchers found an imbalance in the amount of organic carbon and pyrite (a form of sulfur) buried in sediments during the early Cenozoic — a finding that led them to surmise that during that period carbon was primarily buried in swamps rather than deposited in the ocean as it is today.

Toward the end of this period, temperatures became warmer, turning the swamps into enormous beds of dry, carbon-rich peat. The researchers hypothesize that the peat beds caught fire and may have burned for thousands of years, releasing huge amounts of carbon into the atmosphere and leading to an event known as the Paleocene-Eocene thermal maximum (PETM), a 10,000-year-long period at the end of the early Cenozoic characterized by extremely high temperatures.

Models indicate that the rate of carbon release during the PETM is roughly the same as the rate at which human activities add carbon to the atmosphere today. Although the time frames differ (10,000 years for the PETM; 100 years for the release of man-made atmospheric carbon), the parallel has led some earth scientists to believe that this ancient event is analogous to the global warming occurring on Earth today.

The researchers cite a parallel event in recent history, when El Nino conditions in 1997 and 1998 caused a period of extremely dry weather and drought. The enormous forest and peat fires that raged in Indonesia during this time released massive amounts of carbon into the atmosphere, and resulted in the largest annual increase in atmospheric carbon dioxide in half a century.

Kurtz and his colleagues hope to confirm their theory by further investigations, which may reveal increased charcoal deposition in coal deposits and sediments from this era.

The research was recently published in Paleoceanography (Vol. 18, No. 4) and reviewed in the March 11 issue of the journal Nature.