表儿茶素能提高内皮里 的可用量，但怎么提高才是这条链真正的一环。内皮里的 NO 有一个产量、有一个损耗，表儿茶素被认为两头都动了一下。
产量这一头。 造 NO 的是内皮细胞里的一台酶，叫内皮型一氧化氮合酶（eNOS）。它平时是半停着的，需要被磷酸化（在酶身上挂一个磷酸基团，相当于把开关从待机拨到工作档）才全速运转。在细胞实验里，表儿茶素能推动这一步，于是同样一批酶，单位时间放出的 NO 更多。
损耗这一头。 NO 出厂之后要穿过一段距离才到平滑肌，路上如果撞见超氧阴离子（一种带着多余电子、见谁抢谁的），两者几乎瞬间反应掉，NO 还没到岗就没了。血管有炎症、血糖长期偏高、抽烟的人，超氧阴离子多，NO 就这样被半路吃掉。早先的解释是，黄烷醇在血里直接替 NO 把超氧阴离子清除掉；但吃下去之后血里的黄烷醇浓度很低，远不够和超氧阴离子硬碰硬，这个说法现在站不住。更可能的是，它压低了血管壁里制造超氧阴离子的酶（ 氧化酶）：源头少造一点，NO 半路损失就少一点。
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Miller, K. B., Hurst, W. J., Payne, M. J., Stuart, D. A., Apgar, J., Sweigart, D. S., & Ou, B. (2008). Impact of alkalization on the antioxidant and flavanol content of commercial cocoa powders. Journal of Agricultural and Food Chemistry, 56(18), 8527-8533. Natural (non-alkalized) cocoa powder had the highest flavanols and antioxidant capacity; alkalization (Dutch processing) sharply reduced flavanols, with heavy alkalization losing the majority. 10.1021/jf801670p
Ried, K., Fakler, P., & Stocks, N. P. (2017). Effect of cocoa on blood pressure. Cochrane Database of Systematic Reviews, 4, CD008893. Meta-analysis of ~40 RCT comparisons (~1,804 participants) found flavanol-rich cocoa lowered blood pressure by a small amount (systolic ~1.8 mmHg), attributed to flavanol-driven endothelial nitric oxide. Abstract: 35 trials (40 comparisons, 1,804 mainly healthy participants) lasting 2 to 18 weeks (mean 9); SBP -1.76 mmHg (-3.09 to -0.43) and DBP -1.76 mmHg; about -4 mmHg systolic in people with hypertension and no significant difference in normotensive people; moderate-quality evidence for a 'small (2 mmHg)' effect 'in the short term'. The abstract does not test the nitric-oxide mechanism (abstract, PMID 28439881). 10.1002/14651858.CD008893.pub3
Sansone, R., Rodriguez-Mateos, A., Heuel, J., Falk, D., Schuler, D., Wagstaff, R., et al. (2015). Cocoa flavanol intake improves endothelial function and Framingham Risk Score in healthy men and women: a randomised, controlled, double-masked trial (the Flaviola Health Study). British Journal of Nutrition, 114(8), 1246-1255. Twice-daily cocoa flavanols (~450 mg each) improved flow-mediated dilation and lowered estimated cardiovascular risk in healthy adults, using purified high-dose flavanols rather than chocolate. 10.1017/S0007114515002822