Sun May Prevent Some Kinds of Cancer
Study finds lower death rates from breast, colon cancer with higher exposure
THURSDAY, April 4, 2002 (HealthDayNews) -- For years, the message from the medical community has been to stay out of the sun if you want to prevent skin cancer.
While that advice hasn't changed, a new study suggests sun exposure may not be all bad. In fact, the study found the sun might actually help prevent death from some cancers.
In the report, published in this month's Occupational and Environmental Medicine, researchers from the National Cancer Institute found people who worked outdoors and lived in a sunny part of the country were less likely to die from breast or colon cancer than those who worked indoors or lived in less sunny climates.
In the study, the authors suggest vitamin D may play a role in reducing the risk of death from these cancers. Sun exposure causes the body to produce vitamin D, and the authors explain that previous studies have shown vitamin D may slow cancer cell growth.
However, they caution the results from this latest study are preliminary, and it's simply too soon to tell anyone it's OK to get more sun.
"[This study] should not be used as a basis for changing sun behavior, particularly because sunlight is known to contribute to skin cancer," says study author Dr. Michal Freedman, an epidemiologist at the National Cancer Institute. "Instead, the study suggests that there would be value in more sophisticated research that could examine whether there is a relationship between sunlight and breast and colon cancer."
For this study, the researchers examined more than 600,000 death records from 24 different states. They divided the data by cause of death, residential sun exposure, occupational sun exposure, and estimated physical activity from work.
There were five categories for cause of death, and a control group of people who had died of other causes such as heart disease. The five cancer types were non-melanoma skin, breast, ovarian, prostate and colon.
Residential sun exposure was estimated, based on where people lived at the time of their deaths and where they were born. Freedman and his colleagues estimated occupational exposure to the sun by the profession listed on the death certificate.
Not surprisingly, the researchers found the rates of death from skin cancer were higher when people lived in sunnier areas of the country. What was surprising was that the risk of dying from the other four cancers studied was lowest in the sunniest climes.
The researchers also found people who had worked outside in a sunny area of the country were the least likely to die from breast or colon cancer, regardless of physical activity levels on the job.
While he says this is an interesting study, Dr. Roy Shore, chief of the division of epidemiology of environmental medicine at New York University School of Medicine, points out the research has some limitations.
"Whenever you look at some risk factor for cancer and only used data from the deceased, there's concern that there is a bias," explains Shore. "Only 30 to 35 percent of those with breast cancer die from it, so it doesn't represent the whole range of those with the disease."
Also, he says that because the information was gathered solely from death certificates, there is a great deal of information missing about lifestyle factors that could have influenced these results.
Freedman readily acknowledges these weaknesses.
"This is an exploratory study with many limitations, including the lack of good data on lifetime sun exposure, diet, recreational exercise, reproductive history and other factors that could have affected the results, and the necessity of relying on death certificates rather than living subjects," Freedman says.
Freedman hopes the results from this study will be the basis of further research on the possible connection between sunlight, vitamin D, and breast and colon cancer.
What To Do
For information on preventing cancer, go to the Canadian Cancer Society.
To learn more about vitamin D and its possible disease-fighting capabilities, read this information from the National Institutes of Health.