Xeroderma Pigmentosum Society, Inc.

Tips for XP patients: Caffeine concern alleviated

Caffeine for XP patients

by James E. Cleaver, Ph.D.

 

Caffeine is one of the most universal additives to our food and drink. We find it not only in coffee and tea, but also in chocolate bars, many over the counter medicines, soft drinks, and other unexpected places. We like the stimulant, and it provides a welcome jolt to start the day or to keep us awake when necessary. But apart from the "buzz" that benefits all of us, is there anything about caffeine that is special for an XP person? Is it something to be avoided, as you should UV light and other carcinogens such as cigarette smoke.

 

Some XP patients and their families may be concerned about caffeine, because we do use high concentrations of caffeine in some of our laboratory experiments. The combination of caffeine and ultraviolet light can be worse for some types of cells under experimental conditions. This is because caffeine interferes with the signaling molecules that cells use after ultraviolet irradiation. These signals tell a cell it is damaged, and bring into play repair enzymes and other protection and recovery processes. The use of caffeine actually was one of the first laboratory experiments in the 1960's that gave us a clue about DNA repair.

 

David Busch has established a diagnostic service for XP: the assays measure the sensitivity of cells to UV light and how much DNA repair the cells can do. The results diagnose repair deficient XP cells from groups A through G. But XP variant cells have normal sensitivity and normal levels of repair, because they lack a different kind of enzyme involved in recovery from UV damage. These cells are much more sensitive than normal cells to the combined action of UV light and caffeine, and this provides a preliminary diagnosis of an XP variant cell line. But does this mean that XP variant patients should keep off coffee and tea? Not at all; the reason is in the amounts involved.

 

To illustrate the difference between a cup of coffee and an experiment in the lab with caffeine, let's compare concentrations in the two situations. (The detailed calculations are in footnote 1 below.) To get the amount of caffeine we use in an experiment into your body, you would need to drink 100 cups at one go! As few as 2 to 3 cups can already cause tremors of a caffeine overdose. And 50 to 200 cups of coffee contain enough caffeine to kill an adult! The combination of such high levels of caffeine with ultraviolet light exposure is unlikely to be found in any normal circumstance outside of the laboratory.

 

There is little need for concern, therefore, that a few cups of coffee can cause problems for anyone, and the latest EPA list of human carcinogens does not list caffeine, itself (see footnote 2). And, to the best of our present knowledge, we also see no special concerns for an XP patient. With all the other things you have to be concerned about, caffeine, in small amounts, should be among the least.

James E. Cleaver, Ph.D.

UCSF Cancer Center,

University of California, San Francisco, CA. 94143.

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Footnote-calculations

(1) The average cup of coffee has 100 milligrams of caffeine; enough to give us that morning boost. If all the caffeine in a single cup gets distributed, unchanged, throughout our body (say an 80 kilogram adult, of which about 70% is liquid), then the concentration works out to be approximately 10 micromolar. In our experiments we grow cells in
1 millimolar concentrations of caffeine. The difference is a factor of 100.
(2) The EPA carcinogen list can be found at here.

This list of human carcinogens includes at least 200 items, including cigarette smoke, solar and tanning parlor ultraviolet light, but not caffeine, except when it occurs in combinations with phenacetin in analgesics, where any cancer risk may due to other additives.

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