Over the millennia, our ancestors frequently called upon willow bark tea to relieve the minor agonies of sprains, headaches, and menstrual cramps. Around the turn of the century, pharmacologists tinkered with the chemistry of salicin, the brews analgesic ingredient, to make a synthetic analog -- acetylsalicyclic acid, which we know as aspirin.
But willow isnt the only natural product containing an aspirinlike salicylate. Related compounds also show up in tomatoes, pineapples, and many tree-grown fruits. Cooks add them to foods when they mix in a variety of seasonings, such as anise, cayenne, dill, and oregano. Any salad garnished with marigold or clover gets an additional helping. Even wintergreen products and dark teas carry these compounds.
However, with societys increasing consumption of processed foods, most diners will ingest the majority of their foodborne salicylates from synthetic additives, especially flavorings. Because at least some salicylates readily pass through the skin, any present in suntan lotion, cosmetics, perfumes, or topical creams could further boost exposure, notes Lillian May Ingster of the National Center for Health Statistics (NCHS). Indeed, the Maryland Poison Centers salicylates web page lists Ben Gay, the popular muscle rub, as containing 6,000 milligrams of skin-penetrating methyl salicylate per 30 milliliters.
Though most foods appear to contain far smaller quantities of salicylates, in aggregate they may still exert pharmacological effects. At least thats the argument that Ingster and Manning Feinleib now make.
In the September American Journal of Public Health, these NCHS epidemiologists lay out a tantalizing thesis: The growing ubiquity of natural and synthetic salicylates permeating the U.S. food supply may go a long way toward explaining the puzzling decline in heart disease mortality since the mid-1960s. This trend, which they note is seen "among every demographic subgroup of the population," emerged long before physicians began routinely prescribing aspirin to lower risk.
To date, little research has considered heart effects that might be attributable to garden-variety salicylates. The information that has been published does, however, suggest that these compounds compete for the same cellular-binding sites in the body as aspirin and provide many of the same actions as aspirin -- such as relieving pain, fever, and inflammation.
Like aspirin, other salicylates also inhibit an enzyme (cyclo-oxygenase) that has been implicated in a number of processes affecting the circulation, such as the tensing of blood vessels, the stickiness of blood platelets, and presumably the ability of platelets to form clots.
A major difference between aspirin and other salicylates appears to be potency. For instance, the acetyl group that pharmacologists added to create aspirin provides the drug with "the capacity to totally wipe out the clotting ability of a [blood] platelet -- for the life of the platelet. Permanently," Ingster says. The effect of ordinary salicylates on platelets, by contrast, is only temporary.
An individuals total daily dose remains the big unknown because there have been only the most tentative of estimates. Contributing to the problem, Ingster notes, there has been no systematic study of salicylate concentrations in foods nor must food labels even identify the presence of these compounds.
Moreover, manufacturers of synthetic analogs for medical and other uses have stopped publicly reporting their U.S. production figures. Until about 2 years ago, manufacturers had been required by law to submit such figures to the government. However, Ingster learned, when any single company, become dominant source of some product, the government will shield production figures of that product from public records to keep this measure of business activity out of the hands of competing companies.
Apparently, the production of each salicylate (such as salicylic acid, benzyl salicylate, methyl salicylate, and amyl salicylate) fell to a dominant company, Ingster says, because after 1970, data on these disappeared from public records. The previous 40-year trend, however, suggested a steady increase in their production.
All this said, several researchers have attempted to generate ballpark estimates of individual exposures. Their numbers typically run through a range of about 10 to 200 milligrams per day. Though a typical aspirin tablet contains 250 to 500 milligrams, Ingster points out that when it comes to reducing the risk of a fatal heart attack in persons with heart disease, "you only need a very small amount to be therapeutic. Some say that as little as 40 milligrams per day -- which is half a baby aspirin -- is sufficient to provide a protective benefit."
If salicylates should turn out to indeed provide a heart benefit, might we look forward to food processors adding them intentionally -- as a nutraceutical? Thats not likely, Ingster says, because these compounds are widely suspected of being the trigger for asthma and certain other conditions in susceptible persons.
"Ironically," she notes, "I first came on to the issue of salicylates in food about 3 years ago while talking with a good friend who is extraordinarily allergic to them. He explained how he could hardly eat anything off the [grocery] shelf that was processed -- whether ketchup, canned fruit drinks, or mayonnaise -- for fear of running into salicylates."
This caught her attention. Having been a heart-disease epidemiologist for nearly 20 years, she was well aware of the clinical data on aspirins benefits for heart disease. From that point on, she began poring over anything and everything she could find on salicylates.
She and Feinleib argue that their new hypothesis "is attractive because it would go a long way toward explaining . . . the decline in cardiovascular disease mortality [in the early 1960s], which spread through every state." Certainly, "the ubiquity of synthetic salicylates in products ranging from toothpaste to soft drinks, from pasta sauce to ice cream, would make them available to all segments of the population."
Variations in how they have been adopted might even help explain some of the geographic and ethnic differences in heart disease risk, they claim. For instance, the American Heart Association and other groups have been advocating adoption of a "Mediterranean" style diet -- one that relies on fresh fruits, salads, olive oil dressings, and whole-grain breads. Well, theres plenty of salicylates in many fruits, tomatoes, and the spices that go into dressings. Indeed, Ingster muses: "If you take Italian salad dressing with thyme and oregano, and mix it with vinegar, which is acetic acid, maybe in the stomach it will turn into acetylsalicylic acid" -- which is aspirin.
"I realize this is carrying speculation to the extreme," she laughs. But if it gets people to start investigating this whole idea a little more seriously, she says, then maybe it wasnt such a crazy idea after all.
Table prepared by L.M. INGSTER.
Canned tomato sauce
Hot paprika powder
Dry thyme leaves
Twinings Darjeeling tea
These measured values have been gleaned from published accounts and compiled by L.M. Ingster.
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Lillian May Ingster
National Center for Health Statistics
6525 Belcrest Road, Room 1000
Hyattsville, MD 20782
This week's Food for Thought is prepared by Janet Raloff, senior editor of Science News.