What is the best way to take a fat-soluble vitamin? The answer depends on which vitamin you’re talking about. Each fat-soluble vitamin needs to be combined with varying levels of fats for efficient absorption. To make matters more complicated, different vitamins react differently when combined with certain food types.
Let’s take a look at the four major fat-soluble vitamins and the best ways to maximize their absorption in the body.
The word vitamin was first used by Polish biochemist Casimir Funk in 1911. At the Lister Institute in London, Funk identified a compound that prevented inflammation of the nervous system in chicken fed a diet deficient in that compound. He named the compound as ‘vitamine’ because he believed that the compound was essential for life and must be an amine. Later the last letter ‘e’ was removed from ‘vitamine’ when it was discovered that the vitamins do not necessarily have to be amines.
Fat-soluble vitamins are those that dissolve themselves in fats and oils. These vitamins are absorbed in fats present in food and stored in the body’s fatty tissues. Sources of fat-soluble vitamins include plants, animals, and dietary supplements. There are a total of 4 fat-soluble vitamins—A, D, E, and K. These vitamins follow the same absorption mechanism as fat and oils.1 Fat-soluble vitamins are either stored in the liver or released in the bloodstream and used by various tissues.
Among the four important fat-soluble vitamins, A, D, and K work synergistically with each other and with magnesium, an essential mineral. Vitamin D3, vitamin K, magnesium, zinc, and calcium work in tandem. If you are deficient in one of these vitamins or minerals, you should consume the others too to get optimum benefit.
Like other fat-soluble vitamins, vitamin K is incorporated in mixed micelles (aggregate of molecules in the liquid colloid) with the help of bile and pancreatic enzymes and absorbed in the small intestine.
A research article published in British Journal of Nutrition in 2009 studied the absorption of free 13C-labeled phylloquinone, or vitamin K1, with three test meals formulated according to the dietary cluster identified in the UK. More phylloquinone tracer was absorbed with a heart-healthy (termed cosmopolitan) or animal-based meal than with a meal consisting of fast food (termed convenience meal). The fast-food meal contains a similar fat concentration but has a twofold higher polyunsaturated fatty acid (PUFA) content. It is evident from the research findings that vitamin K absorption depends largely on PUFA contents rather than total fat concentration.
In the same study, the bioavailability of phylloquinone from within the food matrix of 3 dietary cluster test meals relative to the 13C-labeled tracer was measured. Researchers found that the absorption of phylloquinone was more than three times better in the convenience meal (where 80% phylloquinone was present in oil phase) compared to the other meal patterns where phylloquinone is present in the vegetable matrix.5 These findings support the fact that absorption efficiency of phylloquinone from fortified oil is better than from vegetable matrix.
After reading the findings of the above research articles, it becomes obvious that we require a moderate amount of fat to absorb fat-soluble vitamins.
A study published in Journal of Molecular Nutrition and Food Research demonstrated that consumption of pulses like kidney beans, white beans, chickpeas, green or brown lentils, and flageolets reduced the bioaccessibility of beta carotene—a precursor of vitamin A—by up to 65%, of retinyl palmitate—a synthetic form of vitamin A—by up to 69%, 45% of vitamin D, 53% of vitamin E, and 67% of vitamin K compared to the test meal containing potatoes. This is due to the binding ability of pulse fiber and other compounds such as phytates, saponin, and tannins. It is advisable to avoid eating pulses along with fat-soluble vitamin-rich foods or supplements for better bioabsorption.6
Different fat-soluble vitamins have different roles in human physiology.7
Vitamin A overdosing is common in the United States. A study found that toxic or excess levels of vitamin A are more of a concern than its deficiency. The tolerable upper intake level of vitamin A is 3,000 mcg RAE (retinol activity equivalents).8 It will be difficult to reach that level by consuming food alone, but some multivitamin supplements contain a high amount of vitamin A in the form of retinol. Retinol is the greatest concern for toxicity. Vitamin A is stored in the liver, and the body can release it as needed. So, before swallowing a high-dose multivitamin pill, make sure it does not cross the tolerable limit. The best way to check this is with a random blood test done by your physician or at your nearest clinic.
Vitamin D is found naturally in animal foods such as fatty fish, egg yolks, liver, and butter. Although the best source is sufficient exposure to sunlight, it depends upon the length of UV radiation, its intensity (which gets affected by pollution of the atmosphere), and skin pigmentation.
Vitamin D overdose is less common than vitamin A overdose. To keep yourself healthy, you should check your vitamin D level twice a year to maintain an optimal clinically recommended concentration in the blood. To get the maximum benefit of vitamin D, you must maintain a vitamin D level of 40 ng/mL, and to achieve that you need around 5,000-6,000 IUs of vitamin D3 per day, or an even higher dose from food, sunlight exposure, and/or vitamin D3 dietary supplements.
The best way to ensure that you are getting the optimal dose of vitamin E in a form your body can absorb is to make smart dietary choices. As there are limited natural resources found for vitamin E that are also affected by seasonal variations, you may take a natural or organic dietary supplement to fulfill your requirement. An overdose of Vitamin E may occur if it consumed at a dose of more than 400 IUs/day, which may lead to hemorrhagic stroke. The best way to check that you are absorbing the Vitamin E through food or supplements correctly, and it is remaining in an active form inside your body, is to get a blood test or consult a physician.