To the Editor:
Horcajada-Molteni et al.(1) previously reported that rutin (quercetin-3-0-rutinoside) inhibits ovariectomy-induced osteopenia in growing rats. Furthermore, they claim that rutin partially explains the effect of vegetables on bone metabolism, which was found in an earlier study.(2) This claim, however, is not justified because only a single pharmacologic dose of rutin was used by Horcajada-Molteni et al.(1)
Indeed, these authors used a diet in their experiment containing 0.25% rutin. The mean daily food consumption was 14.5 g throughout the study. Thus, the daily intake of rutin was 36.2 mg/rat. We have shown that the daily ingestion of 1 g of dried onion, added to the daily food, inhibits bone resorption by 20% and increases bone mineral content by 18%.(2) The quercetin content of the onion powder we used (measured after acid hydrolysis) was 2.93 mg/g (P. C. H. Hollman, unpublished results, December, 1997) Thus, the daily intake of rutin from 1 g of onion was six times less compared with the study of Horcajada-Molteni et al.(1) Moreover, leeks and wild garlic, which also inhibited bone resorption similarly to onion,(2) have a content of quercetin, after acid hydrolysis, of 0.022 mg/g and 0.025 mg/g dry matter (P. C. H. Hollman, unpublished results, April, 1998), respectively. Thus, leeks and wild garlic significantly inhibited bone resorption despite the fact that they provided a daily rutin intake which is 800 and 700 times lower, respectively, than the dose used by Horcajada-Molteni et al.(1) Taken together, these results show that the study of Horcajada-Molteni et al.(1) can neither explain the effect of onion, a vegetable exquisitely rich in rutin, on bone metabolism nor the effect of other vegetables because their rutin content may be very modest.
These findings suggest that the claim raised by Horcajada-Molteni et al.(1) that their results “partly explain the beneficial effect of common vegetables against osteopenia” is not warranted. For such a claim to be valid an effect of realistic doses of rutin as it occurs in natural foodstuffs should be used. Thus, before these data are available, epidemiologists should avoid to take the dietary intake of rutin from vegetables as a factor affecting bone metabolism.