[PubMed] [JNeurosci] [PubMed] 90
The dividing line between what we call soluble and what we call insoluble is arbitrary, but the following are common criteria for describing substances as insoluble, soluble, or moderately soluble
Adding random fourth and fifth peptides on top of a prescribed blend, because of a podcast or a forum post, is not optimization
Here's the TL;DR on vitamin timing: while there is no official medical advice dictating that you should take vitamin supplements at a specific time of day to improve their efficiency, there is quite a lot of research showing that avoiding some vitamin supplements at particular times (or more accurately, with particular meals) can improve absorption, or that taking some vitamins alongside food can reduce the risk of adverse side effects
A few in-vitro and animal studies suggest copper peptides may support collagen synthesis or growth factor signaling, but human clinical trials specifically examining hair growth outcomes are limited