I agree that relatively small improvements in public health could potentially be highly beneficial. Research on this might be totally tractable. 

What I am concerned might be intractable is deploying results. Public health (and all health-relevant products) is a massive industry, with a lot of strong interests pushing in different directions. It seems entirely possible that all the answers are already out there, just drowned out by food, exercise, sexual health, self-help, and other industries.

There's so much noise out there, it seems unlikely that a few EAs will be able to get a word in edgewise.

I was reminded of that post recently when reading Why We Sleep by Matthew Walker, who described the significant benefits that things as simple as switching away from LED lighting could have on sleep quality, which in turn has enormous impact on cognitive performance, mental health, car accidents, etc. I started to think that further investments in sleep research could potentially have high societal returns.

It's worth noting that Walker's book significantly misrepresents the science. Quoting at length from Guzey:

In the process of reading the book and encountering some extraordinary claims about sleep, I decided to compare the facts it presented with the scientific literature. I found that the book consistently overstates the problem of lack of sleep, sometimes egregiously so. It misrepresents basic sleep research and contradicts its own sources.

In one instance, Walker claims that sleeping less than six or seven hours a night doubles one’s risk of cancer – this is not supported by the scientific evidence (Section 1.1). In another instance, Walker seems to have invented a “fact” that the WHO has declared a sleep loss epidemic (Section 4). In yet another instance, he falsely claims that the National Sleep Foundation recommends 8 hours of sleep per night, and then uses this “fact” to falsely claim that two-thirds of people in developed nations sleep less than the “the recommended eight hours of nightly sleep” (Section 5).

Walker’s book has likely wasted thousands of hours of life and worsened the health of people who read it and took its recommendations at face value (Section 7).

The myths created by the book have spread in the popular culture and are being propagated by Walker and by other scientists in academic research. For example, in 2019, Walker published an academic paper that cited Why We Sleep 4 times just on its first page, meaning that he believes that the book abides by the academic, not the pop-science standards of accuracy (Section 14).

Any book of Why We Sleep’s length is bound to contain some factual errors. Therefore, to avoid potential concerns about cherry-picking the few inaccuracies scattered throughout, in this essay, I’m going to highlight the five most egregious scientific and factual errors Walker makes in Chapter 1 of the book. This chapter contains 10 pages and constitutes less than 4% of the book by the total word count.

Hmm I sort of agree with this. I think when I run back-of-the-envelope calculations on the value of information that you can gain from "gold standard" studies or models on questions that are of potential interest in developed-world contexts (eg high-powered studies on zinc on common cold symptom, modeling how better ventilation can stop airborne disease spread at airports, some stuff on social platforms/infrastructures for testing vaccines, maybe some stuff on chronic fatigue), it naively seems like high-quality but simple research (but not implementation) for developed world health research  (including but not limited to the traditional purview of public health) is plausibly competitive with Givewell-style global health charities even after accounting  for the 100x-1000x multiplier.

I think the real reason people don't do this more is because we're limited more here on human capital than on $s. In particular, people with a) deep health backgrounds and b) strong EA alignment have pretty strong counterfactuals in working or attempting to work on either existential biorisk reduction or public health research for developing world diseases, both of which are probably more impactful (for different reasons).