This week, I received a call from a client asking if orange juice could increase his risk of skin cancer. He had just heard a story on the local news, which drew its conclusion from a recent research study published in the Journal of Oncology. With cases like this, it's easy to see why there is so much confusion about nutrition. One day fruits like oranges are good for you, and the next day they are linked to melanoma, a deadly skin cancer?
As a registered dietitian, I always like to dig into the actual source behind the claim in the popular media. Here is my angle and though process:
Can this be biologically plausible at all?
Oranges along with other foods such as figs, grapefruit, celery, parsley, etc. contain a naturally occurring chemical called psoralens. Psoralens actually are used in medicine to treat eczema, psoriasis and even occasionally cutaneous T-cell lymphomas. However, psoralens are not all good. Psoralens are activated by sunlight and can cause cell damage, potentially and theoretically leading to skin cancer.
This study is considered a prospective cohort study. In other words they observed a specific population for a certain amount of time. In this case, the population observed was nurses and doctors from the Nurse’s Health Study and Physician’s Health Study. Diet information was collected every 2 to 4 years and the subjects were followed for 24 to 26 years. Researchers examined health outcomes and compared it to the information they gathered from diet questionnaires.
The study found that people who consumed citrus fruits or juice more frequently, were more likely to develop melanoma. Those who consumed citrus twice per week or less did not have an increased risk; those who consumed citrus two to four times per week had a slight increased risk but it was not statistically significant; those who consumed citrus five to six times per week had a 26% increased risk and those who consumed citrus more than 1.6 times per day had a 36% increased risk. Further analysis found that people who consumed grapefruit more than three times per week had a 41% increased risk and those who consumed orange juice versus whole oranges had an increased risk as consumption increased. Researchers also found that the risk of developing melanoma was highest among people who had higher number of sunburns or spent more time in direct sunlight during childhood and adolescence.
The study gathered its diet information through food frequency questionnaires asking questions about what people ate and the quantity of what people ate over the previous year. It is possible that people did not report 100% accurately due to lapses in memory. Also, people had to rely on memory for questions about sunburn and sun exposure during childhood and adolescence. In addition, the study only looked at a specific population: health professionals between the ages of 30 and 55 years. There were more than double the amount of women than there were men. Non-white participants were excluded. We cannot say that these results apply to everyone. The study did not control for location. This could make a big difference for a few reasons. First, people in Florida for example are likely to have more total sun exposure than people living in a colder region like Vermont. In addition, many of these warmer climates also are more conducive to growing citrus. Someone living near an orange grove is more likely to eat oranges more often than someone who does not. Ultimately, we cannot say that the results apply to everyone and just because there is a correlation does not mean there is causation.
Where do we go from here:
Citrus can be a great source of cancer fighting phytochemicals like vitamin C, hesperidin and pectin. Until further research is done, we cannot draw any conclusions. The results of this study are anything but conclusive. However, until we reach that point, if you have a family history of melanoma, have extremely fair skin or high exposure to the sun, I would ditch the orange juice, grapefruit/grapefruit juice and aim to consume citrus fruits twice per week or less. Also, check out my skin cancer reduction tips on my next blog post to be proactive in your health and skin care.