Many dietary flavonoids possess anti-cancer activities. Here, the effect of apple peel flavonoid fraction 4 (AF4) on the growth of triple-negative (MDA-MB-231, MDA-MB-468), estrogen receptor-positive (MCF-7), and HER2-positive (SKBR3) breast cancer cells was determined and compared with the effect of AF4 on normal mammary epithelial cells and dermal fibroblasts. AF4 inhibited breast cancer cell growth in monolayer cultures, as well as the growth of MCF-7 spheroids, without substantially affecting the viability of non-malignant cells. A sub-cytotoxic concentration of AF4 suppressed the proliferation of MDA-MB-231 cells by inhibiting passage through the G₀/G₁ phase of the cell cycle. AF4-treated MDA-MB-231 cells also exhibited reduced in vitro migration and invasion, and decreased Akt (protein kinase B) signaling. Higher concentrations of AF4 were selectively cytotoxic for MDA-MB-231 cells. AF4 cytotoxicity was associated with the intracellular accumulation of reactive oxygen species. Importantly, intratumoral administration of AF4 suppressed the growth of MDA-MB-231 xenografts in non-obese diabetic severe combined immunodeficient (NOD-SCID) female mice. The selective cytotoxicity of AF4 for breast cancer cells, combined with the capacity of sub-cytotoxic AF4 to inhibit breast cancer cell proliferation, migration, and invasion suggests that flavonoid-rich AF4 (and its constituents) has potential as a natural therapeutic agent for breast cancer treatment.

YouTube has gained popularity as a social media platform providing free access to nutrition information. We aimed to assess the credentials of popular YouTube nutrition content creators, whether evidence was cited in their videos, and if they were financially incentivized through sponsorships. We sampled the 10 most-viewed videos of the top 40 nutrition-related YouTube channels ( n = 400 videos). We recorded the training credentials of the content creators along with the presence of scientific references and financial sponsorships, comparing differences between credentials. Of the videos sampled, 22.50% were by content creators with medical doctor (MD) or registered dietitian (RD) training, 42.00% cited references, and 17.75% had sponsorship. MDs (5.00%) had more videos containing references compared to non-MD content creators (mean proportion 1.00 vs. 0.39, p < 0.0001), with most references being specific (the source clearly provided) (1.00 vs. 0.09, p < 0.0001). Content creators with MDs/RDs/nutritionist credentials used more references (0.55 vs. 0.22, p < 0.0001 compared to those without. The mean proportion of sponsored videos by MDs/RDs was 0.10 compared to 0.23 for other content creators ( p = 0.09). These findings suggest that YouTube content creators’ credentials may be related to the likelihood that reference citations and financial conflicts of interest are present in nutrition-related videos.