Vegans had better worry about their B12. The rest of us, on western diets, need worry about very little except for Vitamin D in winter (or if you insist on never exposing yourself to sunshine in summer). As for B vitamins, unless you're one of those very fussy people who refuse to eat your greens, you'll get all you need from your diet. Those non-greens eaters should maybe worry slightly about folic acid (folate, or Vitamin B9), especially if they're thinking of getting pregnant. The supplements industry never ceases to incense me. The vast majority of people never need supplements of vitamins and minerals. A varied diet which includes good-quality veg is all we need in that regard. Never join the ranks of the worried well...