Bioavailability refers to the proportion of a nutrient that is absorbed and utilized by the body(1). When it comes to vitamins and minerals, not all forms are created equal—some are more bioavailable than others. This means that your body can absorb and use them more effectively, ensuring you get the most out of your multivitamin and supplements. In this comprehensive guide, we'll explore the bioavailability of 19 common vitamins and minerals, highlighting the most and least bioavailable forms of each nutrient.
Which Forms Are Most Bioavailable?
1. Vitamin A
Vitamin A is a fat-soluble vitamin crucial for vision, immune function, and reproduction(2). It exists in two forms: preformed vitamin A (retinol) and provitamin A carotenoids (such as beta-carotene). Preformed vitamin A, found in animal products like liver and fish, is more bioavailable than provitamin A carotenoids, which are found in plant-based foods like carrots and sweet potatoes(3). This is because the body can more easily convert retinol into its active form, while it must first convert beta-carotene into retinol(4). While beta-carotene bioavailability is generally lower than that of preformed vitamin A, it is still a valuable source of vitamin A, especially for vegans and vegetarians.
- Least bioavailable: Provitamin A carotenoids (e.g., beta-carotene)(4)
- Most bioavailable: Preformed vitamin A (e.g., retinol)(3)
2. Vitamin B1 (Thiamine)
Thiamine is a water-soluble vitamin essential for energy metabolism and nerve function(5). It is found in foods like whole grains, legumes, and lean meats. The most common form of thiamine in supplements is thiamine hydrochloride, but thiamine mononitrate and benfotiamine are also available(6). Research suggests that benfotiamine, a fat-soluble form, has higher bioavailability than thiamine hydrochloride and thiamine mononitrate, due to its enhanced absorption and retention in the body(7).
- Least bioavailable: Thiamine hydrochloride, thiamine mononitrate(6)
- Most bioavailable: Benfotiamine(7)
3. Vitamin B2 (Riboflavin)
Riboflavin, another water-soluble B vitamin, is involved in energy production and antioxidant defense(8). It is found in foods like dairy products, meat, and green leafy vegetables. Riboflavin-5'-phosphate is the active form of riboflavin in the body, and studies show that it has higher bioavailability than regular riboflavin when taken as a supplement(9).
- Least bioavailable: Riboflavin(9)
- Most bioavailable: Riboflavin-5'-phosphate(9)
4. Vitamin B3 (Niacin)
Niacin, also known as vitamin B3, plays a vital role in energy metabolism and the synthesis of fatty acids and cholesterol(10). It is found in foods like meat, fish, and whole grains. The two main forms of niacin in supplements are nicotinic acid and niacinamide(11). Both forms appear to have similar bioavailability, but niacinamide is less likely to cause flushing, a common side effect of high-dose nicotinic acid supplementation(12).
- Least bioavailable: Neither form has significantly lower bioavailability(12)
- Most bioavailable: Both forms have similar bioavailability, but niacinamide may have fewer side effects(12)
5. Vitamin B5 (Pantothenic Acid)
Pantothenic acid, a water-soluble vitamin, is essential for the synthesis of coenzyme A and the metabolism of fats, carbohydrates, and proteins(13). It is found in a wide variety of foods, including meat, whole grains, and vegetables. Calcium pantothenate is the most common form of pantothenic acid in supplements and is considered highly bioavailable(14).
- Least bioavailable: Not applicable, as calcium pantothenate is the primary form used in supplements(14)
- Most bioavailable: Calcium pantothenate(14)
6. Vitamin B6 (Pyridoxine)
Vitamin B6, another water-soluble B vitamin, is crucial for amino acid metabolism, neurotransmitter synthesis, and immune function(15). It is found in foods like meat, fish, and whole grains. Pyridoxal-5'-phosphate (P-5-P) is the active form of vitamin B6 in the body and is considered more bioavailable than pyridoxine hydrochloride, the most common form found in supplements(16). However, pyridoxine hydrochloride is still a useful form of vitamin B6 that occurs in food and can be used as a dietary supplement, as it is still comparably bioavailable.
While some studies suggest P-5-P has a higher bioavailability because it is the active form of vitamin B6, other studies show that pyridoxine hydrochloride is also well-absorbed and bioavailable. The body can convert pyridoxine hydrochloride into the active P-5-P form(47). Thus, both forms can be considered useful in dietary supplements, but more research is needed to determine if one form is significantly more bioavailable than the other.
- Least bioavailable: Neither form has significantly lower bioavailability(16)
- Most bioavailable: Pyridoxal-5'-phosphate (P-5-P) and pyridoxine hydrochloride are comparably bioavailable(16)
7. Vitamin B7 (Biotin)
Biotin, also known as vitamin B7, is a water-soluble vitamin essential for energy metabolism, fatty acid synthesis, and maintaining healthy hair, skin, and nails(17). It is found in foods like eggs, nuts, and seeds. Biotin supplements typically contain pure biotin, also known as D-biotin, which is considered highly bioavailable(18).
- Least bioavailable: Not applicable, as pure biotin is the primary form used in supplements(18)
- Most bioavailable: Pure biotin (D-biotin)(18)
8. Vitamin B9 (Folate)
Folate, or vitamin B9, is crucial for DNA synthesis, cell division, and the metabolism of amino acids(19). It is found in foods like green leafy vegetables, legumes, and fortified grains. Folic acid, the synthetic form of folate, is commonly used in supplements and fortified foods. However, not everyone can efficiently convert folic acid into its active form, L-methylfolate, due to genetic variations(20). As a result, L-methylfolate is considered more bioavailable for those individuals(21).
Least bioavailable: Folic acid (for individuals with genetic variations)(20)
Most bioavailable: L-methylfolate(21)
9. Vitamin B12 (Cobalamin)
Vitamin B12 is essential for DNA synthesis, red blood cell production, and the maintenance of a healthy nervous system(22). It is found in animal products like meat, fish, and dairy. Methylcobalamin and cyanocobalamin are the two main forms of B12 found in supplements. Methylcobalamin, the active form of B12 in the body, is considered more bioavailable than cyanocobalamin, which must first be converted into methylcobalamin(23).
- Least bioavailable: Cyanocobalamin(23)
- Most bioavailable: Methylcobalamin(23)
10. Vitamin C (Ascorbic Acid)
Vitamin C is a water-ssoluble antioxidant that plays a crucial role in collagen synthesis, immune function, and iron absorption(24). It is found in fruits and vegetables, particularly citrus fruits, strawberries, and bell peppers. Ascorbic acid is the most common form of vitamin C in supplements and is considered highly bioavailable(25). However, some individuals may prefer Ester-C, a buffered, non-acidic form of vitamin C, which has been shown to have similar bioavailability and may be gentler on the stomach(26).
- Least bioavailable: Neither form has significantly lower bioavailability(26)
- Most bioavailable: Ascorbic acid and Ester-C have similar bioavailability(26)
11. Vitamin D
Vitamin D is a fat-soluble vitamin essential for calcium absorption, bone health, and immune function(27). It is found in a few foods, like fatty fish and fortified dairy products, and can also be synthesized by the body when exposed to sunlight. Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are the two main forms of vitamin D found in supplements. Research shows that vitamin D3 is more bioavailable and effective at raising blood levels of vitamin D than vitamin D2(28).
- Least bioavailable: Vitamin D2 (ergocalciferol)(28)
- Most bioavailable: Vitamin D3 (cholecalciferol)(28)
12. Vitamin E
Vitamin E is a fat-soluble antioxidant that protects cell membranes from oxidative damage(29). It is found in foods like nuts, seeds, and vegetable oils. There are eight forms of vitamin E, but the most biologically active and bioavailable form is alpha-tocopherol(30). When choosing a vitamin E supplement, look for natural d-alpha-tocopherol, as it is more bioavailable than synthetic dl-alpha-tocopherol(31).
- Least bioavailable: Synthetic dl-alpha-tocopherol(31)
- Most bioavailable: Natural d-alpha-tocopherol(31)
13. Vitamin K
Vitamin K is a fat-soluble vitamin involved in blood clotting and bone health(32). There are two main forms of vitamin K: vitamin K1 (phylloquinone), found in green leafy vegetables, and vitamin K2 (menaquinone), found in fermented foods and animal products. Research suggests that vitamin K2 is more bioavailable and has a longer half-life in the body than vitamin K1, making it more effective at supporting bone and cardiovascular health(33).
- Least bioavailable: Vitamin K1 (phylloquinone)(33)
- Most bioavailable: Vitamin K2 (menaquinone)(33)
Calcium is a vital mineral for bone health, muscle function, and nerve transmission(34). It is found in foods like dairy products, leafy greens, and fortified foods. Calcium carbonate and calcium citrate are the two most common forms of calcium in supplements. While both forms are effective, calcium citrate is generally considered more bioavailable, especially for those with low stomach acid levels or absorption issues(35).
- Least bioavailable: Calcium carbonate(35)
- Most bioavailable: Calcium citrate(35)
Iron is an essential mineral involved in oxygen transport, energy production, and immune function(36). There are two types of iron in food: heme iron, found in animal products, and non-heme iron, found in plant-based foods and supplements. Heme iron has higher bioavailability than non-heme iron, as it is more easily absorbed by the body(37). When it comes to non-heme iron supplements, iron bisglycinate is considered more bioavailable and less likely to cause gastrointestinal side effects than other forms like ferrous sulfate(38).
- Least bioavailable: Non-heme iron (e.g., ferrous sulfate)(38)
- Most bioavailable: Heme iron and iron bisglycinate(37)(38)
Magnesium is a crucial mineral for nerve and muscle function, energy production, and bone health(39). It is found in foods like nuts, seeds, whole grains, and leafy greens. Magnesium supplements come in various forms, such as magnesium citrate, magnesium glycinate, and magnesium oxide. Research indicates that magnesium citrate and glycinate have higher bioavailability than magnesium oxide due to their enhanced absorption(40).
- Least bioavailable: Magnesium oxide(40)
- Most bioavailable: Magnesium citrate and magnesium glycinate(40)
Selenium is an essential trace mineral that plays a critical role in DNA synthesis, thyroid hormone metabolism, and antioxidant defense(41). It is found in foods like Brazil nuts, seafood, and meat. Selenomethionine and selenite are two common forms of selenium found in supplements. Studies suggest that selenomethionine has higher bioavailability than selenite due to its improved absorption and retention in the body(42).
- Least bioavailable: Selenite(42)
- Most bioavailable: Selenomethionine(42)
Zinc is an essential mineral involved in immune function, protein synthesis, and wound healing(43). It is found in foods like meat, shellfish, and legumes. Zinc supplements come in various forms, including zinc picolinate, zinc citrate, zinc acetate, zinc gluconate, zinc monomethionine, zinc oxide, and zinc glycinate. The bioavailability of these forms can vary based on scientific research.(44)
- Least bioavailable: Zinc gluconate and zinc oxide(44)
- Most bioavailable: Zinc picolinate, zinc citrate, zinc acetate, zinc monomethionine, Zinc glycinate(44)
Copper is a vital trace mineral that plays a role in energy production, iron metabolism, and antioxidant defense(45). It is found in foods like shellfish, nuts, and seeds. Copper supplements typically contain copper gluconate, copper sulfate, or copper amino acid chelates. While all three forms appear to have similar bioavailability, copper amino acid chelates may be better absorbed and utilized by the body(46).
- Least bioavailable: Neither form has significantly lower bioavailability(46)
- Most bioavailable: Copper amino acid chelates(46)
When it comes to choosing the most effective vitamins and minerals for your body, understanding the bioavailability of different forms is crucial. By selecting the most bioavailable forms of each nutrient, you can ensure that you're getting the most out of your multivitamins and supplements, optimizing your overall health and well-being.