This piece appeared in The Hindu this morning – Understanding How Ayurveda Works. The Hindu does have a soft corner for “complementary and alternative medicine” (CAM), but normally it’s limited to the writings of B.M. Hegde in the “open page”, where anyone can write in. This is different – it appeared in the Science and Technology section.
The piece starts with a list of differences between what it calls “traditional medicine (TM)” and “modern medicine (MM)”. Including this: “TM looks at results, not how the treatment works while MM advances by understanding the mechanism of action, and cause and effect.” This is a convenient trope in CAM – convenient because it absolves CAM proponents from explaining how their drugs do what they’re claimed to do. The rest of the article describes a study done on 2 ayurvedic preparations which was published about two years ago in PLOS ONE – “In Vivo Effects Of Traditional Ayurvedic Formulations in Drosophila melanogaster Model Relate with Therapeutic Applications”.
The scientists did an experiment on the effects of these formulations on fruit flies – one formulation is based on amla (gooseberry), the other contains mercury sulphide. As if often the case with CAM substances, their supposed benefits are multitudinous – one “enhances life expectancy, body strength, intellect, fertility and gives freedom from illness”, and the other is used “in a wide variety of disorders including chronic and recurrent infections (pneumonia/bronchitis), fistula-in ano, rheumatological diseases especially those of auto-immune origin, sexual and general debility and benign and malignant neoplasms”. With an aim of analysing “effects of the whole Ayurvedic formulations rather than their “active” components”, the scientists tested the fruit flies for “effects on longevity, development, fecundity, stress-tolerance, and heterogeneous nuclear ribonucleoprotein (hnRNP) levels”.
The problem is plausibility – no plausible mechanism for these substances to have these effects is given, other than a routine mention of anti-oxidants. Science-based medicine looks at plausibility because the prior probability of a drug working makes a big difference to such studies. This article – The Plausibility Problem – explains pretty much everything you need to know on the subject, including things like true/false positives/negatives, what we mean by power and specificity of a study, prior probability and positive predictive value. (Also see this other article on science-based vs. evidence-based medicine.) This is essentially Bayesian reasoning. In a nutshell, a low prior probability matters:
Even for a well designed, powerful study, if the premise is highly unlikely, a positive result does not give us convincing evidence that the premise is true. For studies with weaker power, the results are even less persuasive. So why do extraordinary claims require extraordinary evidence? Because for implausible claims, ordinary evidence is highly unreliable. A single positive study with a P value of .05 is ordinary evidence. For a very implausible hypothesis, a result of this sort is quite likely to be a false positive.
So without any hypothesis on how amla and mercury sulphide have these beneficial effects on “life-history”, this single study cannot be taken as proof that they have these effects. The vagueness of the supposed benefits is problematic too (and is a common trope in CAM with its descriptors like “holistic”, “boosts immunity”, “removes toxins”, “promotes well-being”). The more specific the claimed benefit, the easier it is to test it. (Compare the ayurvedic vagueness with the highly specific benefits and mechanisms of gooseberry listed here.)
Here’s a contrasting example also from “ancient” medicine – the anti-malarial drug Artemisinin. Artemisinin comes from the herb Artemisia annua, and its anti-malarial properties were first described by Tu Youyou and colleagues in the 1960s when Chinese scientists investigated more than 2,000 herbal recipes found in traditional Chinese medicine. So far so good – ayurveda proponents would be happy reading this. But read a bit more and the differences start to appear – the active compound was identified, the original extraction method didn’t work, only three treatments emerged while the rest were useless (I wonder if ayurveda proponents would do such a culling instead of making blanket assertions like “Ayurveda works”), even more powerful derivatives and combination treatments have been synthesized (i.e. they’re not “natural”), and crucially, the chemical mechanism of the drug is mostly known. This is a good example of Bayesian principles applied to medicine – the combination of a good prior probability and an overwhelming amount of data confirms that the drug works.
So what the scientists investigating ayurvedic substances should do is: (1) propose mechanisms i.e. HOW does the substance do what they claim it does and (2) do proper repeated trials to gather evidence that it does do what they say it does.