Vitamins that promote weight loss include vitamin B-12 and vitamin D, according to Mayo Clinic and SFGate respectively. However, as of 2015, sufficient evidence to back these claims does not exist.
Vitamin B-12 helps reduce body weight by increasing metabolic rate and body energy, notes Mayo Clinic. However, people with sufficient vitamin B-12 in their blood may not experience the increase in body energy due to the vitamin. One way to get vitamin B-12 is to eat fish and meat. One way to obtain vitamin D is to bask in the sun, states SFGate. However, excessive vitamin D intake is harmful to the body and may cause body weakness and nausea accompanied with vomiting.