A new US study based on laboratory mice suggests that drinking low to moderate amounts of caffeine and exercising regularly protects the skin from damaging ultraviolet rays known to cause skin cancer. The caffeine and exercise appear to work together to kill off precancerous skin cells whose DNA has been damaged by ultraviolet B (UVB) rays. The discovery is yet to be tested in humans.
The research took place at Susan Lehman Cullman Laboratory for Cancer Research at Rutgers University Ernest Mario School of Pharmacy in the state of New Jersey, and is published as an early online edition in the Proceedings of the National Academy of Sciences (PNAS).
Skin cancer triggered by sun exposure is the most common type of cancer in the United States, with over 1 million cases being diagnosed each year, according to the National Cancer Institute.
In this experimental study the researchers, led by Dr Allan Conney, Director of Rutgers’ Cullman Laboratory, put hairless laboratory mice into four groups. One group drank caffeinated water (equivalent to a human drinking one or two cups of coffee a day). Another group of mice took voluntary exercise on a wheel. The third group drank caffeinated water and exercised, while the fourth (the control group) had no caffeine and did not exercise.
All the mice were exposed to UVB light from laboratory lamps.
The scientists found that all four groups of mice had DNA damage in their skin cells with varying degrees of apoptosis or programmed cell death. However, the mice that drank caffeine and exercised showed the most skin cell apoptosis compared to the control group.
Apoptosis is a series of biochemical events that leads to the death of a cell so its remnants can be safely disposed of (unlike traumatic cell death). When the DNA in a cell is badly damaged the cell can become cancerous, unless it triggers this “cell suicide”, as Conney explained:
“If apoptosis takes place in a sun-damaged cell, its progress toward cancer will be aborted.”
“The differences between the groups in the formation of UVB-induced apoptotic cells (those cells derailed from the track leading to skin cancer), were quite dramatic,” he added.
Conney and colleagues were able to compare the extent of apoptosis in the four groups of mice by looking for physical changes in the skin cells and counting levels of biochemical markers such as caspase-3, an enzyme involved in programmed cell death, and p53, a tumour suppressor.
Compared to the UVB exposed control group, they found that:
- The caffeine drinking group of mice had a 90 per cent increase in apoptosis induced by UVB,
- The exercise group had a 120 per cent increase, and
- The caffeine and exercise group had a nearly 400 per cent increase.
The researchers attributed the dramatic difference between the caffeine and exercise group and the others to “some kind of synergy” between the caffeine and exercise that is working at the biochemical level. And while they could speculate as to what that might be, it is still a mystery that warrants further investigation, and eventually also doing human tests.
“We need to dig deeper into how the combination of caffeine and exercise is exerting its influence at the cellular and molecular levels, identifying the underlying mechanisms.”
“With an understanding of these mechanisms we can then take this to the next level, going beyond mice in the lab to human trials. With the stronger levels of UVB radiation evident today and an upward trend in the incidence of skin cancer among Americans, there is a premium on finding novel ways to protect our bodies from sun damage,” he added.
“Voluntary exercise together with oral caffeine markedly stimulates UVB light-induced apoptosis and decreases tissue fat in SKH-1 mice.”
Yao-Ping Lu, Bonnie Nolan, You-Rong Lou, Qing-Yun Peng, George C. Wagner, and Allan H. Conney.
PNAS Published ahead of print July 30, 2007
Written by: Catharine Paddock