A new US study of over 110,000 people found that the more caffeine there was in their diets, the lower their risk of developing basal cell carcinoma, the most common type of skin cancer.

The researchers write about their findings in the 1 July issue of the journal Cancer Research.

However, lead investigator Dr Jiali Han, associate professor at Brigham and Women’s Hospital, Harvard Medical School in Boston and Harvard School of Public Health, told the press:

“I would not recommend increasing your coffee intake based on these data alone.”

But, Han explained, their finding does add basal cell carcinoma to a growing list of diseases that increasing coffee intake appears to lower the risk of, such as type 2 diabetes and Parkinson’s disease.

Basal cell carcinoma or basal cell skin cancer is the most common cancer in the US, and most skin cancers are of this type. The cancer starts in the top layer of the skin, the epidermis and usually results from regular exposure to sunlight or other ultraviolet radiation.

Even though it is a slow-growing cancer and is not life-threatening like melanoma, it causes considerable morbidity and places a burden on health systems, says the American Association for Cancer Research.

Also, because of the large numbers of newly diagnosed cases, anything that has a protective effect, such as changes to diet, can have an impact on public health, said Han.

For their prospective study, Han and colleagues used data on 112,897 people taking part in the Nurses’ Health Study, and the Health Professionals Follow-up Study, both large and long-running studies into factors that affect health.

Of the participants, just over 22,700 developed basal cell carcinoma over 20 years of follow up.

Han and colleagues found that the more caffeine participants consumed, the lower their risk of basal cell carcinoma (BCC):

“The amount of caffeine intake from all dietary sources was inversely associated with BCC risk,” they write.

When they ranked the participants according to caffeine consumption, with the highest consumption at the top and the lowest at the bottom, they found for women, the top 20% of caffeine consumers had an 18% lower risk of BCC than the bottom 20%. For men, the risk was lower by 13%.

The researchers also found a similar, significant link when they looked at caffeinated coffee only, as opposed to caffeine from all sources.

Drinking 3 cups of caffeinated coffee was linked to a 21% lower risk of developing BCC in women and a 10% lower risk in men, compared to drinking less than 1 cup per month.

And caffeine from other dietary sources also had a similar effect: the higher the intake, the lower the risk of BCC.

Decaffeinated coffee, on the other hand, was not linked to a similar decrease in BCC risk, write the authors.

Han said their findings really suggest it is the caffeine in coffee that is having this effect.

The findings support studies on mice that suggest caffeine may somehow block the formation of skin tumors.

But Han said more studies are now needed, in different populations, and exploring the underlying biology, before we can be sure of this.

In contrast to the results for BCC, Han and colleagues found no inverse association between caffeine intake and risk of melanoma or squamous cell carcinoma.

However, Han said this could be because there weren’t sufficient numbers of these types of skin cancer in their figures.

“As the study participants are followed for a longer time, the number of cases of these conditions is likely to increase. We may be in a position in 10 years’ time to better address this issue,” said Han.

Related reading: Drinking Coffee: More Good Than Harm? (9 July 2012).

Written by Catharine Paddock PhD