Where are you seeing vitamin D supplements for $10/year? That’s several orders of magnitude less than most OTC supplements.

A Google search for vitamin d results in ads, ahem "sponsored results", for 180 servings for $27, which is about $55 for a full year assuming it's one serving per day, which is the same decimal order of magnitude as $10 (but, I suppose, since we are on HN, is three or four orders of magnitude in binary)