Some vitamins and nutrients are found in abundant quantities in meat, poultry and fish but not in plant-based foods (unless they have been "fortified," i.e., nutrients have been added). For this reason, vegetarian or vegan diets may not meet all the daily nutrient requirements, and supplements may be necessary. This may occur with vitamins B-12 and D, iron, zinc, calcium, iodine, long-chain omega-3 fatty acids and, possibly, protein.
Below are strategies for meeting daily nutrient requirements through dietary modifications or supplementation, and ways to find supplements that don't contain ingredients objectionable to people following vegetarian or vegan diets.
Vitamin B-12 is found most abundantly in meats, poultry and fish. Although cereals, milks and yogurts that are fortified with B-12 may provide sufficient B-12 for vegetarians, unfortified, plant-based foods are generally not good sources. Consequently, people who are strict vegetarians or vegans may need to supplement with vitamin B-12. A 3-month study among vegans and vegetarians with marginal B-12 deficiency showed that supplementing with 50 mcg of sublingual B-12 daily or 2,000 mcg weekly could restore adequate B-12 levels.
Keep in mind that B-12 will get absorbed just as well as from an oral tablet as sublingual tablets, and sublingual tablets and other specialty forms often contain sugar substitutes that can cause gas, bloating or diarrhea. See our Top Pick among B-12 supplements.
Most people are able to meet their daily nutrient requirement for iron by eating foods such as meat, poultry, and fish, as well as dried fruits, grains, and green leafy vegetables. However, since iron from plant sources is absorbed half as well as that from animal sources, strict vegetarians or vegans may need to consume almost twice as much iron from their foods, as other people, and this may be hard to get from foods alone.
If you need to supplement with iron to meet your daily nutrient requirements, see our Top Pick among iron supplements.
Be aware that iron supplementation can cause constipation, nausea, diarrhea, stomach erosions and ulcers, so it is a good idea to have your hemoglobin and ferritin levels checked by your doctor before starting an iron supplement.
Compounds called phytates occur in legumes and grains and can interfere with zinc absorption. Consequently, vegetarians and vegans may require as much as 50% more of the RDA for zinc than non-vegetarians. The RDA of zinc for adults is 11 mg for men and 8 mg for most women (women who are pregnant or breastfeeding need more), so men and women following a vegetarian or vegan diet may need closer to 17 mg and 12 mg daily, respectively, if obtained exclusively from food.
Fortunately, following a well-planned vegetarian or vegan diet that includes good food sources of zinc and includes steps to reduce phytate intake should be sufficient to meet zinc requirements. Foods that are rich in zinc include soy, nuts, seeds and fortified cereals (Saunders, Med J Aust 2013). Although legumes, which are an important source of zinc, also contain phytates, some steps can be taken to reduce phytates in these foods. For instance, soaking legumes before cooking can help reduce the amount of phytate in these foods. Canned beans have been found to have phytate levels 70% to 90% lower than found in dried beans. However, be aware that soaking rice and other grains can lower phytate levels but also reduce levels of zinc by up to 30% (Lestienne, Food Chem 2005).
If you do need to take zinc supplements long-term to meet your daily nutrient requirements, it is generally considered advisable to also take copper at a dose of 1 to 3 mg daily, as excessive intake of zinc can interfere with the absorption of copper, leading to copper deficiency. See our Zinc Review for zinc supplements Approved by ConsumerLab that are suitable for vegans and vegetarians.
While calcium can be obtained from various vegetarian- and vegan-friendly foods, including soybeans, white beans and tofu, some research has found that vegan diets are associated with inadequate calcium intake (Clarys, Nutrients 2014). Another study found that middle-aged and older women (but not men) who followed a vegan diet and did not take supplemental calcium and vitamin D had three times the risk of hip fracture compared to non-vegetarians.
Consequently, for vegans (or vegetarians) whose dietary intake of calcium is not adequate (RDA of calcium for adults is 1,000 mg daily for women up to 50 and men up to 70, and 1,200 mg daily for older men and women), it might be a good idea to supplement with a moderate amount of calcium — but no more than 300 to 500 mg per serving. See our Top Picks for calcium supplements, which include some that are vegan-friendly.
While adequate vitamin D can be often be obtained simply through adequate sun exposure, factors such as skin pigmentation, clothing coverage and sunscreen use, age, and location (latitude) of an individual can affect the extent of skin production of vitamin D. Some research has found that following a vegan or vegetarian diet that does not include vitamin D supplements or fortified foods is associated with low vitamin D intake and low blood levels of vitamin D (Craig, J Am Diet Assoc 2009). Consequently, vitamin D supplements may be necessary for some individuals.
Vitamin D can be found in dietary supplements in the D2 or D3 form. Either form can be obtained inexpensively, and both can raise blood levels of vitamin D, although some, but not all, research suggests that vitamin D3 may be more effective. The D2 form may also cause erroneously low vitamin D blood test results. For these reasons, if you need to take a vitamin D supplement, it seems prudent to use the D3 form.
Be aware that vitamin D3 in supplements is often synthesized from lanolin (an animal source) and sold in capsules made from gelatin (also from animals), and thus may not be suitable for vegans. However, some vitamin D3 supplements contain D3 from lichen, which is vegan-friendly although it may be more expensive. You can find such a product in our Vitamin D Supplements Review.
Omega-3 fatty acids
The only type of omega-3 fatty acid that is considered essential is ALA (alpha-linolenic acid), and vegans and vegetarians tend to get sufficient amounts, as it is found in seeds oils, such as flaxseed oil.
Although not considered essential, two other omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are generally obtained from oils from marine sources, such as fish, krill, and algae. These may have benefits due to their anti-inflammatory properties. Vegetarians tend to consume limited amounts of EPA (<5 mg daily) and DHA if eggs are excluded from the diet (Davis, Am J Clin Nutr 2003). See our Top Pick for getting omega-3s from algal oil.
For more details about forms of omega-3 fatty acids for vegans and vegetarians, see our CL Answer about vegan-friendly sources of EPA and DHA.
Iodine is necessary for proper functioning of the thyroid gland, which regulates metabolism in our bodies, and is also necessary for normal brain development in children during pregnancy and infancy. Fish and other seafoods, as well as dairy foods, are good sources of iodine. Fortunately, so are seaweeds, such as kelp, and iodized salt.
Just be aware that if you are using kelp as a source of iodine, one absorbs only about half as much iodine from kelp as from an iodine supplement containing potassium iodide. Also, note that most specialty salts are not iodized.
See the amounts of iodine we found in kelp and other seaweed products — but also note the amounts of toxic heavy metals we found.
Both vegetarians and vegans (including those who are athletes) can meet protein requirements with plant proteins. However, protein needs might be somewhat higher for vegetarians or vegans whose main source of dietary protein are those that are less well digested, such as some cereals (such as corn, oat or rice cereals) and legumes (Craig, J Am Diet Assoc 2009). For these individuals, a protein supplement may be beneficial.
Although many protein supplements are based on whey and casein protein, which are derived from milk and not suitable for vegans and some vegetarians, plant-based proteins such as soy, rice, pea and hemp can be good choices. See our Protein Supplements Review for our Top Picks among protein supplements, including those suitable for vegans and vegetarians. Also see our article about protein supplements for vegans.