Looking at the figures in the paper, cooking for 4 minutes (which is way overkill for spinach leaves) decreases lutein by 25-50% (with relatively large error bars).
I haven’t done the math in how much lutein is in spinach vs how much we need but to a first order of approximation that’s acceptable.
In the abstract they say they cooked spinach for up to something absurd like 60 minutes. Spinach leaves are cooked within a minute or so in my experience, so not sure why they performed the study that way.
Cooking spinach for an hour is something that I suppose might happen if you're making a puréed soup with spinach, and you don't think to put the spinach in at only the last minute.
I also like to cook it from freeze-dried (which I buy from northbaytrading).