This article was first published in
Usually, the questioner has seen or heard something, often through social media, about a loathsome substance that is set to destroy their life or about one that promises to improve their health 鈥渘aturally.鈥� The answer to the question is almost always 鈥渘o, it isn鈥檛 true, but ... The reason for the qualifier is that science isn鈥檛 white or black, it is best seen as several shades of gray.
Generally, I first try to explain what we really mean when, in a scientific context, we claim to 鈥渒now鈥� something. It almost never means that we are absolutely certain. I say 鈥渁lmost,鈥� because there are some certainties: The Earth is not flat. It orbits the sun. Carbon-13 鈥� but not carbon-12 鈥� is radioactive. A hammer and a feather will fall with the same speed in a vacuum. A dog cannot mate with a cat to produce progeny.
However, when it comes to what science says about matters of health and longevity, the answer to 鈥渋s it true that?鈥� is rarely an unqualified 鈥測es鈥� or 鈥渘o.鈥�
When asked whether it is true that a glass of orange juice contains roughly the same amount of sugar as a glass of Coca-Cola, the answer is a definitive 鈥測es,鈥� because this can be proven with chemical analysis. The answer to whether that glass of Coke contains cocaine is for all practical purposes a 鈥渘o,鈥� but nuanced. While the coca leaves used to prepare Coke鈥檚 famous formula 7X have had their cocaine content removed, it is possible that inconsequential traces are left behind. Is true that rat poison is being added to tap water? Yes, but obviously with a qualifier. Sodium fluoride is added to tap water to reduce the incidence of cavities, which it does effectively, and was indeed once used as a rat poison. Of course, not at the same dose!
The question of dose is at play almost every time 鈥渋s it true?鈥� arises. Especially when it comes to carcinogenicity.
Is it true that [blank] causes cancer is one of the most common questions I am asked. It is usually triggered by an article that describes a substance being listed by the International Agency for Research on Cancer (IARC) as a possible, probable or known human carcinogen. You can fill in that blank with bacon, hair dyes, artificial sweeteners, red meat, alcohol, formaldehyde, parabens, glyphosate or a host of other substances.
It is critical to understand that the IARC classification is based on an analysis of 鈥渉azard鈥� as opposed to 鈥渞isk.鈥� A hazard is something that has the potential to cause harm. Risk is the likelihood that it actually does. Listing a substance in IARC鈥檚 Group 1 means that there is strong evidence that the substance can cause cancer, but it says nothing about how likely it is to do so.
Ultraviolet light, a component of sunlight, illustrates the difference between hazard and risk. Light can be thought of as being composed of packets of energy called photons. The impact of a photon on a molecule of DNA can cause a mutation that triggers an irregular multiplication of cells, cancer. X-rays are also made up of photons, but these are more energetic than the photons of ultraviolet light, so they are more likely to damage DNA. Although both sunlight and X-rays are in Group 1, X-rays are clearly more capable of triggering cancer than sunlight.
But exposure matters. A single chest X-ray is not a problem, but repeated baking in the sun is. More photons of lower energy can have a greater effect than fewer photons of greater energy. Then there is individual liability. A person with dark skin is less at risk for developing skin cancer than someone with pale skin, even at the same ultraviolet light exposure.
When it comes to IARC鈥檚 鈥減ossible鈥� and 鈥減robable鈥� carcinogens, the situation is even more complex because these rankings are not based on evidence gleaned from humans but on laboratory experiments with cell cultures or on rodent feeding studies in which the animals are exposed to much higher doses than people can ever experience.
How then, does one answer the question about whether it is true that potato chips cause cancer, as I was recently asked. The question was stimulated by an 鈥渋nfluencer鈥� with no scientific background whose social media post warned against eating chips because they contain the carcinogen acrylamide.
Indeed, acrylamide does form when potatoes are fried, and this compound is classified as a 鈥減robable human carcinogen鈥� by IARC based on feeding it to rodents in large doses. It is therefore capable of causing cancer, which means that it is hazardous. But it is not necessarily risky. That depends on how much is eaten and what the rest of a person鈥檚 diet is composed of.
Conceivably, chips as a regular part of the diet may trigger cancer, but an occasional indulgence is likely harmless. The roasting of coffee beans also produces acrylamide, but it is quite clear that coffee is not carcinogenic. If it were, that would have revealed itself epidemiologically. No increased risk of cancer has ever been noted in coffee drinkers.
Then there are questions that are not about possible harm, but about possible benefits.
Can blueberries reduce the risk of cancer? Does oat bran lower blood cholesterol? Is berberine 鈥渘ature鈥檚 Ozempic?鈥� Can eating tomatoes or watermelon alleviate depression? Blueberries contain a variety of polyphenols that can neutralize the notorious, potentially cancer-causing free radicals that form in the body as a result of inhaling oxygen. But that is in a test tube. Oat bran can reduce cholesterol somewhat, but you have to eat about a cup a day, which is a challenge. Berberine is a plant extract that does stimulate the release in the gut of the appetite suppressant hormone GLP-1, the same hormone that is mimicked by the active ingredient in Ozempic. However, the effect of berberine is very small and no clinical trials have shown significant weight loss with its use.
The tomato and watermelon claim traces to a Chinese study that found lycopene, the natural red colouring in these fruits, capable of enhancing synaptic plasticity, the brain鈥檚 ability to form new connections that are crucial for memory, learning and emotional stability. The problem is that this was seen in male mice with stress-induced depression fed daily doses of lycopene equivalent to that found in 21 tomatoes and 14 cups of watermelon. So, no, it isn鈥檛 likely that depression in humans can be alleviated by eating tomatoes or watermelon.
Obviously, simple 鈥測es鈥� or 鈥渘o鈥� answers to questions pertaining to health risks and benefits are elusive. But there is one point that can be made with confidence: When it comes to answers to such questions, the devil is in the details.
