Re: Consumption of spicy foods and total and cause specific mortality: population based cohort study
The effect shown certainly appears plausible: people eating Chili pepper die less. The mechanism is unclear but is very probably not related to systemic effects of capsaicin, which has thankfully no bioavailability: in an (unpublished) study in 6 healthy volunteers, the ingestion (oral) of up to 20 mg pure capsaicin did not result in any measurable plasma presence of capsaicin (HPLC-UV, 100 ng/ml detection threshold). Believe me, you do not want to go above. This is consistent wiith experimental studies finding a cancer preventive effect of injected but not oral capsaicin in animals. Since capsaicin is a potent neurotoxin, it is indeed a good thing that it has no systemic bioavailability. The reason for this was not explored: no intestinal resorption, complete liver first pass effect? My bet is on complete liver metabolization, since capsaicin is lipid soluble.
So the effects found may relate to interactions with the intestinal vanilloid receptors, changes in the intestinal microbiota, or other reasons, such as the antibiotic or antiseptic effect of chilli: non-ingestors of capsaicin maybe eating more toxic or contaminated foodstuffs. Since the study was done in a single region, with the same alimentation, it could well be a valid explanation. It might be interesting to compare the effect of capsaicin on survival across cultures: Would the French who use little capsaicin live shorter lives than those Chinese who use a lot? Among Chinese, do the Sichuan Chinese live longer than others? Do French from the Basque region around Espelette (a particularly delicious chili) live longer than those from Alsace or Brittany?
Competing interests: I tend to put a lot of chili pepper in food (especially Espelette chili) when I cook, and my family complains of it. I will now be able explain why it is Good to do so.