Plant compounds and antioxidants: Evidence-Based Supplement Guide

More antioxidants are not always better during training. In a randomised trial of 54 young adults, daily vitamin C and E supplements during 11 weeks of endurance training blunted muscle markers of new mitochondria (PMID 24492839). Fitness and running gains were similar to placebo, and the authors advised caution with antioxidant supplements alongside endurance training (PMID 24492839). The body makes its own antioxidants, including glutathione. In a small study, older adults had lower glutathione than younger adults, and two weeks of its building blocks cysteine and glycine restored it and lowered markers of oxidative stress (PMID 21795440). Broccoli contains glucoraphanin, which becomes sulforaphane when the plant enzyme myrosinase reaches it, for example when broccoli is chewed (PMID 31590459). Three-day-old broccoli sprouts held 10 to 100 times more glucoraphanin than the mature plants (PMID 9294217). Sulforaphane is the most cited natural activator of Nrf2 signalling, according to a review of the field (PMID 31590459). Curcumin, a compound from the spice turmeric, is poorly absorbed, and the body breaks it down and clears it quickly (PMID 17999464).

1. **Think twice about high-dose antioxidant supplements during endurance training.** They blunted training adaptations in muscle in a randomised trial (PMID 24492839). 2. **Get plant compounds from food first.** Chewing broccoli brings glucoraphanin into contact with myrosinase, which forms sulforaphane (PMID 31590459). 3. **Broccoli sprouts are a concentrated source of glucoraphanin** (PMID 9294217). 4. **Expect little curcumin to be absorbed from turmeric alone** (PMID 17999464).

The antioxidant trial ran for 11 weeks of training (PMID 24492839). The glutathione study supplemented for two weeks (PMID 21795440).

- **The glutathione study was very small**, with eight older and eight younger adults (PMID 21795440). - **The antioxidant trial measured muscle markers and fitness**, and fitness gains were similar to placebo (PMID 24492839). - **The sprout figures come from a plant analysis**, and the same paper's other findings were in rats (PMID 9294217). - **How much sulforaphane reaches the body depends on the food or supplement form**, which the review examines (PMID 31590459). - **The curcumin paper is a review of absorption**, not a trial of benefits (PMID 17999464). - **No dose appears in this guide.** Dosing is a clinical decision and is held for clinician review. - **This guide has not been reviewed by a clinician.** `reviewStatus` above says so.

- **Antioxidant supplements can work against training adaptations** (PMID 24492839). - **Concentrated plant extracts are not the same as food.** Ask a pharmacist or clinician before combining them with medicines.

No ingredient is linked from this guide. It covers how antioxidants and plant compounds behave in the body, and it does not point to a product.

| PMID | Title | | --- | --- | | 24492839 | "Vitamin C and E supplementation hampers cellular adaptation to endurance training in humans: a double-blind, randomised, controlled trial" | | 21795440 | "Deficient synthesis of glutathione underlies oxidative stress in aging and can be corrected by dietary cysteine and glycine supplementation" | | 31590459 | "Broccoli or Sulforaphane: Is It the Source or Dose That Matters?" | | 9294217 | "Broccoli sprouts: an exceptionally rich source of inducers of enzymes that protect against chemical carcinogens" | | 17999464 | "Bioavailability of curcumin: problems and promises" |