Salicylic acid is best known as an ingredient of Aspirin, but it is a phytohormone, a plant hormone, involved in photosynthesis and many other biochemical processes of plants, not at least their immune system.
Considering this as a vitamin is not mainstream, to put it mildly, but a small group of people do refer to salicylic acid as Vitamin S. For the moment I want to remain impartial regarding the technical question whether or not this is a vitamin, but I tend to see it as an essential substance, a nutrient we need. This is an opinion that gradually gains recognition as knowledge advances.
The known effects on humans are numerous, the most important being that
- it is anti-infammatory, and inflammatory processes are involved in most serious illness - even cancer often starts as an inflammation.
- it is anti-cancerous. It blocks certain processes in tumour growth.
- it is anti-diabetic.
- it probably (not yet conclusively proved) prevents Alzheimer's disease.
Some of this has to do with its effects on prostaglandins, which are substances that are involved in all processes of the body. That is also a danger of a moderate overdose, you don't want to block the whole prostaglandin synthesis, then you'll block too many processes. A strong overdose might lead to intoxication and several serious side-effects, but that goes for everything - absolutely everything, even water.
Salicylic acid also prevents blood clogging. More than that, it prevents the formation of plaque in certain nervous cells of the brain. That plaque consists mainly of oxidation residue and is involved in the brain's process of ageing.
Salicylic acid as a supplement should not be used at all during pregnancy. There is a small risk that its anti-tumorous power could block the growth of the foetus during one stage of the pregnancy - and there is evidence of its interfering in other ways as well.
Neither should it be taken by people with a pathologically increased risk of bleeding, since it makes the blood thinner and coagulation less efficient. In practice it means that if you start bleeding, it is harder to stop it. This effect is not strong enough to be a any problem for a healthy individual, but can be so in extreme cases, where illness, medication or vitamin deficiency has caused a situation where the tendency to bleed is strongly increased. Otherwise this is a good property which reduces the risk of cardiovascular and circulatory disease.
If you take (acetyl) salicylic acid as a part of your vitamin or supplement regimen, you should keep the dose low. Normally, Aspirin and other medicines containing salicylic acid come in 500 gram tablets. At disease, 1-2 such tablets can be taken 1-3 times per day. As a supplement for healthy individuals, however, a suitable dose is about 1mg per kg body weight each day. There is room for a considerable margin of error there: a good policy for a normally sized adult is to buy 500mg tablets and break each tablet in 5-8 pieces, and take one piece every day.
Unless you treat a specific disease, never take more than 100mg per day. While giving no additional benefit, a higher regular intake would increase the risk for harmful side-effects and unduly acidify the body. More is not better.
In nature, all photosynthetic plants contain some level of salicylic acid. Relatively good sources of natural salicylic acid are fruit and vegetables, especially when unripe. Some herbs and spices contain significant amounts, but the original source of this compound is the bark of the willow tree (Salix), which was used medically against fever and pain already by the Sumerians.
Salicylic acid is also used externally, mainly against acne, but against many other skin ailments as well, and it occurs in many skin care products. It normalises the process of desquamation, which is the process of skin cells being sloughed away and replaced with new cells. In plain language, salicylic acid helps removing dead skin cells and cellular debris.
It has been discovered that zinc deficiency in combination with the intake of salicylic acid can lead to loss of hearing. In studies with rats, such induced hearing loss has been reverted by giving extra zinc. Hearing was fully restored.
An interesting parenthesis here is that salicylic acid promotes rooting and many other processes in plants. This can be favourably utilised in horticulture. There are people who put some Aspirin in the water before watering their plants. To my knowledge, the result of this practice has not been scientifically studied, but there is ample anecdotal evidence supporting it and theoretically it makes sense.
If you give salicylic acid to a cat, it risk to die.
Some people have found this fact astonishing. Given what we know about salicylic acid, however, I'm not surprised. I would go a step further and say that if I didn't know it, I would still expect a cat to die by a dose of salicylic acid, or at least to become very, very ill.
Because salicylic acid is a very potent plant hormone, and cats are carnivores, their digestive and metabolic system cannot handle nutrients from the plant kingdom. And this specific nutrient in concentration functions on a very fundamental biochemical level. (Yet salicylic acid is sometimes given to cats in veterinary medicine, and they may tolerate it if the dose is very low. I would say it is a bad choice though.)
For the same reason it is dangerous to draw conclusions about humans based on medical tests on cats. It works better with rats, whose metabolic system is more similar to ours. They are also more closely related to us. Primates and rodents are genetically cousins, while cats belong to a completely different line. Yet, even results of studies on rats cannot always be applied to humans.
Warning: Note that salicylic acid interacts with certain medicines. If you are on medication, please consult a competent professional before taking salicylic acid at the same time.
(This article is based on material previously published in Meriondho Leo and in my e-book “Nutrients & Dietary Supplements”, 2019.)
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