WASHINGTONSize matters, especially in epidemiologic studies.
The European Prospective Investigations into Cancer and Nutrition
(EPIC) was founded on that principle in 1992, said Elio Riboli, MD,
ScM, MPH.
Since then, the EPIC researchers have recruited 484,000 subjects from
nine European countries for a multicenter, prospective study of the
relationship between dietary, genetic, metabolic, and lifestyle
characteristics and the risk of cancer and cardiovascular disease.
Dr. Riboli, chief of the Nutrition and Cancer Unit of the
International Agency for Research on Cancer, Lyon, France, described
the research project at the 10th Annual Research Conference of the
American Institute for Cancer Research (AICR).
We know that a plant-based diet protects against cancers of the
colorectum, stomach, upper aerodigestive tract, and possibly
others, Dr. Riboli said. We also know that salty foods
raise the risk of stomach cancer and that there is information
suggesting that eating meat increases colorectal cancer risk. But we
need to know more: Which foods? Which vegetables? What is their
chemical and physical structure?
In short, while eat more fruits and vegetables may be
good advice for the public, more detailed information is needed to
determine the role of nutrition in initiating or preventing the
development of many cancers, he said.
An advantage of studying populations across Europe (in Denmark,
France, Germany, Greece, Italy, the Netherlands, Spain, Sweden, and
the United Kingdom) is that wide variations in cancer incidence and
dietary practices can be explored.
For instance, Dr. Riboli said, the breast cancer rate in Scotland is
four times higher than the rate in Sicily or southern Spain, while
the stomach cancer rate is highest in central Spain and northern
Italy and lowest in England.
The EPIC researchers have collected a detailed questionnaire from
each study subject on diet, lifestyle, illness, medication use,
physical activity, alcohol and tobacco use, reproductive and
contraceptive history, and socioeconomic factors. Anthropometric
measurements have also been taken.
The food questionnaire lists 150 to 300 food choices, and a more
detailed inquiry into a 1-day actual diet taken from 7%
of the respondents will cover 3,000 possible food descriptions and
700 recipes tailored for each country. At worst, Dr.
Riboli quipped, we can publish books of recipes, if we fail as
cancer researchers.
To date, the EPIC group has taken blood samples from 387,000
subjects. Blood from each subject is parceled out into 28 small (0.5
mL) plastic straws containing plasma, serum, buffy coat or red blood
cells, and stored in liquid nitrogen for study over the next 10 to 15
years. The storage system is designed to withstand power outages as
long as 4 months without refilling.
EPIC will use these stored biologic samples to measure biomarkers
that will then be correlated with the 17,000 cases of cancer expected
to occur in this cohort by 2002. Prediagnostic levels of steroid
hormones, insulin-like growth factors, and other metabolic factors
will be correlated with inherited genetic susceptibilities.
We are trying to go beyond the black box of epidemiology and
identify mechanisms that lead to cancers, Dr. Riboli said. This
may lead to answers to current puzzles such as whether levels of
eicosapentaenoic acid (EPA) from fish oil are related to cancer risk.
EPA levels have been shown to be higher in Denmark and lower among a
group of vegetarians in Oxford, UK.
These biomarker studies may also lead to improved measurements of
data collected on dietary questionnaires, whose accuracy has long
been debated by nutrition researchers.