Dr. Michael Greger has dedicated his career to studying aging and helping his patients and the general public lead healthier lives.A physician who specializes in nutrition and an author, Greger shares information about how lifestyle choices can impact lifespan and makes recommendations based on research from his books, including 'How Not To Die' and 'How Not To Age,' and via his charity, NutritionFacts.org.
The maximum suggested daily requirement is 4,000 IU per day for healthy adults, according to The Cleveland Clinic.Vitamin B12 supports the function of nerve cells and is needed for red blood cell formation and DNA synthesis.Like vitamin D, it's almost exclusively found in animal products and you can't get it from the sun, meaning vegetarians and vegans are at risk for deficiency.