PHILADELPHIATo date, epidemiologic studies looking for a link between adult diet and cancer risk have proved disappointing. But research focusing on in utero nutrition and preschool and adolescent diet may be more fruitful, suggests Karin Michels, ScD, an epidemiologist and assistant professor of obstetrics, gynecology, and reproductive biology at Harvard Medical School.
She spoke about these critical nutritional time points and their possible link to cancer risk at the 5th Annual International Congress of the Society for Nutritional Oncology Adjuvant Therapy.
Dr. Michels acknowledges that there has not been a lot of research in this area, but there has been some, she said, and animal data do support a role of maternal diet during pregnancy in the development of cancer in the offspring.
She explained that speculation about the fetal origins of breast cancer, for example, has been fueled by the knowledge that breast cells are undifferentiated in utero and therefore are susceptible to increased levels of estrogen, toxins, and growth factors that can operate as car-cinogens.
Interest in the fetal origins of cancer has also been stimulated by work on the fetal origins of other diseases. Dr. Michels pointed to research by Dr. David Barker in England, a pioneer in the search for fetal disease origins, who has published some 300 research papers demonstrating the role of early life events, including nutrition, in the later development of cardiovascular disease, hypertension, and diabetes.
Dr. Barker has found that accelerated growth during childhood is a risk factor for ovarian cancer, she said. Infants who are malnourished in utero often experience accelerated growth during the first and second year of life, accompanied by an increased level of insulin-like growth fact, which has been associated with increased cancer risk.
Several studies have showed an association between high birth weight and breast, prostate, and testicular cancer. Dr. Michels, who gathered data for the Nurses Health Study, said that study showed a direct association between high birth weight and the risk of developing breast cancer later in life. Swedish researchers have made similar observations in regard to breast and prostate cancer, she said.
Thus, she said, current recommendations for maternal weight during pregnancy, which do not stress restrictions on weight gain, may be ill advised. Maybe there should be an upper level given, Dr. Michels said.
Birth weight may be significant because it is, in fact, a marker for other things, Dr. Michels said. Potentially, it is a marker for high estrogen levels or for growth factors or for the maternal diet. Another important question is, what aspect of the maternal diet has an effect? Is it the total caloric intake or the composition of the diet?
The Childs Diet
Moving beyond the maternal diet to infant feeding, important areas for investigation are breast-feeding vs no breast-feeding, formula vs cow milk or soy milk, and whether the timing of the introduction of solid food or the timing of withdrawing breast-feeding has any relation to later cancer risk.
There have been several studies examining the relation between breast-feeding and later cancer risk, Dr. Michels said, but, taken as a whole, results have been inconclusive.
Increased cancer risk was correlated with increased total energy intake in childhood in one study, and the association was even stronger when the data were restricted to non-smoking-related cancers, Dr. Michels commented.
Three retrospective studies of adolescent diet failed to identify any strong association between dietary factors and increased cancer risk, but given the retrospective nature of the studies, poor recall might have influenced the results, Dr. Michels cautioned.