The short version
Vitamin B6 is a coenzyme the body leans on constantly, and its reach is unusually wide for a single nutrient.
Primary source 01 / 03
Vitamin B6 in coenzyme forms performs a wide variety of functions in the body and is extremely versatile, with involvement in more than 100 enzyme reactions, mostly concerned with protein metabolism.
Adults need 1.3 mg a day, rising to 1.7 mg after 51. That is not a hard target on any diet: the federal government's own food-ranking table lists canned chickpeas, at 65% of the Daily Value per cup, ahead of pan-fried beef liver and fresh tuna.
Where it actually comes from
Beyond chickpeas, potatoes carry a quarter of the Daily Value per cup, a medium banana another quarter, and fortified breakfast cereal can cover the same ground in one bowl. Spinach, tofu and mixed nuts add smaller but real amounts. None of this requires a supplement aisle, just a kitchen that already leans on legumes and starchy vegetables.
Primary source 02 / 03
About 75% of vitamin B6 from a mixed diet is bioavailable.
Who actually falls short
The fact sheet's list of groups likely to run low never mentions vegans or vegetarians. It names people with impaired kidney function, people with rheumatoid arthritis and other autoimmune conditions, and people on certain antiepileptic drugs. Isolated B6 deficiency is also uncommon on its own.
Primary source 03 / 03
Isolated vitamin B6 deficiency is uncommon; inadequate vitamin B6 status is usually associated with low concentrations of other B-complex vitamins, such as vitamin B12 and folic acid.
There is no evidence case here for routine supplementation on a plant-based diet built around legumes, whole grains, fruit and vegetables. The open question belongs to kidney disease and autoimmune conditions, which is a matter for a clinician regardless of what anyone eats.