I think it's presumptuous to think that more income equals less stress. More income usually does not fall out of the sky. It usually entails working a more demanding career. It's also true that some people have more money because they are neurotic about finances. I know poor people who do not stress about money and well-off people who are obsessive about finances. You can factor in socioeconomic status just to have another vector of analysis but treating wealth and stress as automatically inverse variables is presumptuous and unscientific.

That's a statistical correlation not a mechanism of causation. You actually need to draw a picture how finances impact breast milk quality.

No offense but what is the reason that having more money in your bank account would have a bigger affect on oligosaccharides than living in a more natural environment? I would think that environment would have a more direct connection to breast milk quality than finances.