What it is
Vitamin D governs calcium absorption and bone health, with growing evidence around immune function and muscle. It's the odd one out among vitamins: your skin makes it from sunlight, and food was never meant to be the main supply.
How much
Reference intakes run around 600–800 IU (15–20 µg) a day from food — set assuming minimal sun. Reality: insufficiency is genuinely common, especially through winter, at higher latitudes, with indoor lifestyles, or with darker skin. This is the one vitamin where a supplement is often the sensible answer — ideally sized by bloodwork rather than guesswork, since it's fat-soluble and accumulates.
How well it's tracked
Poorly through food, and honestly that's the nature of the nutrient: few foods carry meaningful amounts, label coverage is inconsistent, and your sun exposure never appears in a food diary. Expect a low-looking number even on decent days; it's the least "complete" metric the app tracks.
Food sources
Fatty fish (salmon, sardines, mackerel), egg yolks, UV-exposed mushrooms, and fortified dairy or plant milks — fortification does a lot of the world's heavy lifting.
In the app
Vitamin D has its Insights card with contributors — and if you supplement, a D supplement has no macros, so logging it is optional; the bloodwork is the tracker that matters here.