Vitamin Calculator

DFE accounts for the different bioavailability of folate from food vs. supplements. Synthetic folic acid (in supplements and fortified foods) is absorbed at ~85% vs. food folate at ~50%. 1 mcg DFE = 1 mcg food folate = 0.6 mcg folic acid from supplements. The RDA of 400 mcg DFE can be met with 240 mcg of supplemental folic acid.

RAE standardizes Vitamin A potency from different sources. 1 mcg RAE = 1 mcg retinol (animal sources) = 12 mcg beta-carotene (plants) = 24 mcg other pro-vitamin A carotenoids. The IOM shifted from IU to RAE units in 2001 to better reflect actual biological activity.

The daily loss of B12 is small and relatively constant across adults (~2.4 mcg/day matches this need). However, older adults (50+) often have reduced gastric acid production, which impairs B12 absorption from food; the IOM recommends they meet their needs through supplements or fortified foods where B12 is in crystalline (free, easily absorbed) form.

The UL for preformed Vitamin A (retinol) is 3000 mcg RAE/day for adults. Excess preformed Vitamin A is teratogenic (can cause birth defects) and hepatotoxic. Beta-carotene from foods does not have a UL because the body regulates its conversion to retinol. Pregnant women should particularly avoid high-dose retinol supplements.

Most vitamins can be obtained from plant foods, with two key exceptions: Vitamin B12 is virtually absent from plant foods and must be supplemented; Vitamin D3 (cholecalciferol) from animal sources is more potent than D2 from mushrooms, and most plant-based eaters need supplementation or careful sun exposure management.

B1: pork, legumes, whole grains. B2: dairy, eggs, organ meats, almonds. B3: poultry, fish, mushrooms, peanuts. B6: poultry, fish, potatoes, bananas. B9 (folate): dark leafy greens, legumes, avocado, fortified grains. B12: meat, fish, dairy, eggs (none in plant foods).

Sunlight exposure on skin converts 7-dehydrocholesterol to Vitamin D3. A fair-skinned person exposing arms and face for 10–15 minutes at midday (UV index ≥ 3) may synthesize 1000–10,000 IU. However, many factors reduce synthesis: dark skin, sunscreen, winter latitude (above 35°N), age, and time of day. Serum 25-hydroxyvitamin D testing is the only reliable way to assess status.

Vitamin A: night blindness, dry skin, frequent infections. B1: fatigue, nerve damage (beriberi). B12: megaloblastic anemia, peripheral neuropathy, cognitive decline. Folate: macrocytic anemia, neural tube defects in pregnancy. Vitamin C: scurvy (gum bleeding, poor wound healing). Vitamin D: bone pain, muscle weakness, rickets in children. These symptoms typically appear with chronic severe deficiency.

Fat-soluble vitamins (A, D, E, K) are best absorbed with fat-containing meals. B vitamins and Vitamin C are water-soluble and can be taken with or without food, though taking them with food reduces nausea. B12 absorption is improved by spacing multiple small doses rather than one large dose, as intrinsic factor-mediated absorption saturates at ~1.5 mcg per dose.