<div>Fat-Soluble Vitamins: Ensuring Absorption & Conversion</div>

Fat-Soluble Vitamins: Ensuring Absorption & Conversion

Follow @slikkfitness on Facebook, Instagram, Twitter, and TikTok for more

What You Need to Know About Vitamins A, D, E, and K

The requirements for fat-soluble vitamins vary depending on our life stage, but deficiencies abound because we often take them wrong.

Fat-Soluble Vitamins: What You Don’t Know
Back in 1912, a Polish chemist named Kazimierz Funk came up with the theory that scurvy and a few other diseases were caused by deficiencies in certain “vital amines,” a term which was soon shortened to vitamins (even though some of these substances weren’t necessarily amines).
Soon after, he isolated the first one of these vitamins, niacin, followed by thiamine, which he used to treat beriberi, a deficiency disease characterized by loss of muscle function and other not-fun stuff.
By the way, it was originally proposed that these vital amines be called Funkians, which is a name I would have gone all in on. Oh well. Regardless, and with apologies to Kazimierz, I think vitamins are kind of a snore, nutritionally.
I could never get excited about that first-year dietitian-in-training stuff that teaches people that avocadoes, or beets, or whatever, are high in riboflavin, etc. Plus, I had a bad experience with a vitamin supplement when I was a toddler. I got ahold of a bottle of liquid vitamins my mother had accidentally left out and I drank the whole thing. I felt new strength flow through me. I tore apart the bars of my playpen. I glared at our chihuahua and he exploded.
Maybe not. But I did turn all red and get awful sick.
I’ve also got some practical reasons for not being a fan of taking multivitamins in general. First, most are plain ill-conceived as certain vitamins and minerals interact with each other and shouldn’t be taken together. I understand the profit-driven motivation, though: most people don’t have the literal or figurative stomach to take more than one pill a day, especially if it means taking them a certain number of hours apart.
Second, some brands try to stand out from the competition by putting excessive amounts of nutrients in each capsule, as if they were hawking rolls of toilet paper that contained 1,000 sheets instead of 750.
Lastly, most Americans are likely “over-vitaminized,” at least when it comes to some of them. It seems everything’s fortified now. Hell, even our bottled water has vitamins added. (This “over-vitaminizing” isn’t true of most minerals, though, and those deficiencies appear to run rampant.)
However, I’ve lately taken a more sympathetic attitude to the fat-soluble vitamins, namely vitamins A, D, E, and K. It looks like we have shifting requirements for these vitamins, depending on what stage of life we’re in. And, as has always been the case, these vitamins are rather fickle when it comes to their willingness to be absorbed by the body. As such, it’s quite possible many of us have deficiencies in these specific vitamins.
Because of all this, I’ve experienced a renewed interest in them, or at least the fat-soluble ones. Hence this article. In it, I’ll rely mostly on a recent paper authored by Rana A. Youness and her colleagues to detail how chronological age determines our need for these nutrients, along with some specific or semi-specific advice on what you need to do to ensure adequate absorption.

Vitamin A is unlike most of the other vitamins in that it contains a broad group of related nutrients. The two main forms are the retinoids (retinol, retinal, and retinoic acid, all of which are found primarily in animal meats) and carotenes (alpha, beta, and gamma, all of which are found in plants), each of which act as sort of a “pro-vitamin” in that they get transformed into vitamin A through a complex set of chemical reactions.
Foods that have high amounts of the retinoids include beef liver and eggs, while foods that contain large amounts of carotenes include leafy green vegetables, tomatoes, mango, and red bell pepper.
Broadly speaking, vitamin A is implicated in healthy skin, a robust immune system, clear vision, and a robust reproductive system. However, vitamin A appears to take on different functions, depending on which life stage we’re in.
It’s estimated that a lack of vitamin A causes anywhere from half a million to three million cases of irreversible blindness in children every year, and half of them die within 12 months of losing their sight. There’s actually a type of genetically modified rice that contains large amounts of beta carotene (that gets converted to vitamin A) that could save these children, but because it’s a GM food, the technology sits moldering in some warehouse. Oh well. That science be scary stuff.
It’s also estimated that a lack of vitamin A causes night blindness (reversible) in approximately 1% of children between the ages of 24 to 59 months. But aside from ensuring eye integrity, the vitamin also plays a pivotal role in the development of a healthy immune system.
For the first 6 months of life, mother’s milk generally provides an adequate supply of the vitamin (325 micrograms, assuming an average daily consumption of 650 ml of milk). However, needs vary widely as children get older.
Humans grow a lot during this period, obviously, and it taxes their nutrition resources, vitamin A among them. Unfortunately, a deficiency during this life stage could cause problems throughout life since vitamin A, as it does during childhood, prevents against eye damage (night blindness and possibly permanent blindness).
A low vitamin A intake can also inhibit the immune system, cause respiratory problems, promote dysplasia (an abnormal growth of cells), or lead to anemia.
While this might seem like just a bunch of theoretical musing, vitamin A deficiency, according to Youness and her colleagues, is a major problem in adolescents.
Vitamin A continues to play a role in healthy vision during this life stage (and, in fact, all life stages), but deficiencies present additional problems for those in early adulthood and middle age. Without adequate amounts, young adults can be more prone to obesity, while older adults need the vitamin to prevent hip fractures.
General Vitamin A Requirements
Children: Between 325 mcg. and 400 mg.
Teen males: 14-18: 900 mcg.
Teen females: 14-18: 700 mcg.
Adult males: 900 mcg.
Adult females: 700 mcg.
How to Ensure Absorption of Vitamin A
Vitamin A precursors need at least 5 grams of dietary fat for them to be absorbed and converted into vitamin A. That means that pouring a low or non-fat salad dressing onto your salad isn’t going to cut it. Without adequate fat, most of those carotenoids will just pass right through. Without adequate fat, the carotenoids and carotenes that do manage to be absorbed won’t be converted to vitamin A.
Animal studies (Deming, et al. 2000) go so far as to say that a low-fat diet can lead to vitamin A deficiency even when serum blood levels remain constant for the vitamin.

The body synthesizes vitamin D from cholesterol when the skin is exposed to the sun, but since we’ve been taught to cover up like we’re beekeepers and slather any remaining exposed skin with the equivalent of bathroom caulk, this conversion is, at best, hampered and at worst, totally obstructed.
That means that most of us have to rely on dietary sources (fatty fish, eggs, dairy products, etc.) or supplements.
The vitamin plays a crucial role in the development and continuing function of the immune system, in addition to being intimately related to prostate health, bone health, reproductive health, depression and anxiety, and calcium homeostasis.
As was the case for vitamin A, vitamin D plays different roles in different stages of life.
Children who are deficient in vitamin D might be more prone to autism, and they’re more prone to asthma, respiratory tract infections, skeletal abnormalities, and improper neuronal development.
Young people need adequate amounts of vitamin D primarily for bone development, mental health maintenance, and, as is the case with all life stages, proper immune system function.
The functions of vitamin D appear to increase with advancing age. Young adults, as well as those in middle age or beyond, require adequate vitamin D levels to decrease inflammation, decrease the risk of type 2 diabetes, thwart the possible development of MS, alleviate sleep disorders, and, as mentioned, prop up the immune system in general. More recently, levels of vitamin D appear to be inversely associated with the risk of prostate disease.
As far as athletes, vitamin D plays a role in skeletal muscle development, lung function, heart function, and the propagation of more little athletes.
Deficiencies in all ages run rampant, though. Approximately 42% of adults are deficient, while approximately 88% of those over 70 are running on fumes.
General Vitamin D Requirements
Children up to 12 months: 400 IU
People from 1 to 70 years: 600 IU
People over 70: 800 IU
How to Ensure Absorption of Vitamin D
Vitamin D is fat soluble. Without concurrently ingesting some fat, ingesting vitamin D-rich foods or taking a vitamin D capsule won’t do much at all.
Generally speaking, foods high in vitamin D contain all the fat you need. That might not be the case with vitamin D supplements, though. In their case, you need to take them with a fatty meal, but one with a MUFA:PUFA ratio greater than 1.
That means that oils like those from soybean won’t work well because they have a greater amount of polyunsaturated fatty acids (PUFAs) than monounsaturated fatty acids (MUFAs). However, oils like olive and sunflower will. About 5 grams of either will suffice.
Vitamin D also requires adequate magnesium levels. Without it, the vitamin just hangs around like some bum in front of a 7-Eleven. Ordinarily, this magnesium issue might not be that important of a factor, but given that roughly 80% of the American public seems to be deficient in the mineral, it likely IS a big deal.

Vitamin K isn’t a single compound but a family of compounds with the common chemical structure of 2-methyl-1,4-napthoquinone.
These compounds include phylloquinone, commonly known as vitamin K1, and a series of menaquinones, which are commonly grouped together as vitamin K2.
Vitamin K1 is found primarily in green leafy vegetables and plant oils, while K2 is predominantly of bacterial origin and found in small amounts in various animal meats and fermented foods.
The average physician knows about vitamin K because it’s instrumental in making four of the 13 proteins needed for blood clotting, and without enough of it, any wound to your skin will cause you to shoot out blood like a punctured garden hose. Well, maybe not that bad, but you get the idea.
Like its fat-soluble brothers, the needs for it differ according to life stage:
Vitamin K deficiency bleeding (VKDB) is relatively rare in children, but vitamin K serves as a prophylaxis against this condition.
Vitamin K is more important to bone health than hemostasis (clotting, essentially) during this life stage. Adolescents need between 155 and 188 micrograms daily to maintain healthy bone development and an additional 54-62 micrograms is needed for normal hemostasis.
As with the other age groups, vitamin K plays an important role in hemostasis, but beyond that, it can help manage Type 2 diabetes and lower the risk for hip fractures and osteoporosis. However, it can also play a pivotal role in two of the banes of advancing age: cardiovascular disease and, in men, benign prostate growth and even prostate cancer.
Let’s look at cardiovascular disease first. One of the hallmarks of atherosclerosis is vascular calcification. It’s literally the deposition of mineral deposits in the vascular system.
Here’s where vitamin K comes in. Vascular calcification is an inflammation-mediated process where macrophages (a type of large white blood cell that not only kills microorganisms, but also stimulates the production of pro-inflammatory cytokines) promote the “mineralization” of arteries (the right kind of macrophages can also clean up arterial walls, but that’s another story).
Vitamin K (K1, specifically), however, has been shown to suppress the expression of these pro-inflammatory cytokines. More importantly, vitamin K also affects something called “matrix GLA protein” (MGP). The molecule is a potent inhibitor of vascular calcification and its actions are vitamin K-dependent.
Regarding prostate cancer, there’s a relatively new theory out there that posits that varicose veins in the prostate cause the amount of free testosterone in the veins adjacent to the prostate to increase by 130 times, and all this localized free T, once it converts to DHT, invariably causes rampant prostate growth and possibly cancer.
Apparently, much like it does in heart-related matters, a vitamin K deficiency (but in the case of the prostate, a deficiency in K2 and not, apparently, K1) leads to calcification of the middle wall of veins around the prostate, laying the groundwork for these torturous vein formations and subsequent disease.
General Vitamin K Requirements
Children up to 9 years: 1-3 years old, 30 mcg; 4-8 years old, 55 mcg.
9-13 years: 209 to 250 mcg.
14-18 years: 75 mcg.
Adult men: 120 mcg.
Adult women: 90 mcg.
How to Ensure Absorption of Vitamin K
Unlike the other fat-soluble vitamins, vitamin K is a greedy bastard; it needs all the fat it can get. Let’s say you eat a spinach salad but use non-fat dressing. That scenario reduces vitamin K (K1) absorption by about 70%. Vitamin K2 is even hungrier. One study showed that vitamin K2 absorption maxed out at a meal with about 35 grams of fat in it (Uematsu, 1996).
Given its clingy relationship with dietary fat, it’s best to take supplemental vitamin K with the largest, fattiest meal of the day, which is generally dinner.

Vitamin E has many guises. It can present itself as alpha, beta, gamma, and or delta tocopherol and tocotrienols (a type of vitamin with double bonds that possess slightly different superpowers than its sibling). Found in large quantities in legumes, almonds, butter, tomato, and leafy vegetables, along with oils such as safflower, sunflower, and soybean oil, it’s long been thought of just as an antioxidant, but that categorization sells its abilities short.
Again, it serves different purposes in different life stages:
Vitamin E’s main function in childhood seems to be in decreasing the risk of asthma. In fact, several studies recommend its use as a cheap prophylactic for childhood asthma.
Vitamin E pivots in function when children reach adolescence. Here it’s kind of a combination nootropic/PED. One study showed that it caused an improvement in academic performance and students’ physical activity (Alghadir, et al. 2019).
Here’s where vitamin E excels. The vitamin has been linked to improved endothelial function, protection against various common and serious health problems, decreased fracture risk, skin “brightening,” and an overall anti-aging effect.
A warning, though. One relatively recent study showed that vitamin E supplementation among males was linked to prostate cancer (Vivarelli, et al. 2019), so taking more than the recommended amount (below) is discouraged.
General Vitamin E Requirements
0 to 6 months: 4 mg.
7 to 12 months: 5 mg.
1 to 3 years: 6 mg.
4 to 8 years: 7 mg.
9 to 13 years: 11 mg.
Over 14 years: 15 mg.
How to Ensure Absorption of Vitamin E
Generally speaking, vitamin E doesn’t need a lot of dietary fat to be absorbed. Despite that fact, there’s a high degree of vitamin E deficiency in the American population. Here’s the rub: fats with a high unsaturated to saturated fats (e.g., sunflower, safflower, grapeseed oil) increase absorption. However, if you eat too many of those oils (which are, coincidentally, rich in vitamin E), you cause chronic inflammation, which depletes vitamin E stores.
Fat Soluble Funkian Facts
Okay, I’ve thrown a lot of info at you. However, here’s what you should take from this article:
Regarding Vitamin A
This vitamin needs at least 5 grams of dietary fat to be absorbed, so use full-fat dressing on your green, leafy salads. Personally, I wouldn’t supplement with A because most vitamin A supplements contain astronomical amounts, and vitamin A toxicity is a real thing. My only exception to this rule is in taking them as part of a multivitamin, most of which use much smaller amounts than supplements that contain nothing but vitamin A. But I’d much prefer you got your vitamin A from the proverbial well-balanced diet.
Regarding Vitamin D
This vitamin is thought to need about 5 grams of accompanying fat to be absorbed. Olive oil and sunflower appear to work best. However, it’s not that easy. You also need to have a calcium-to-magnesium ratio of about 2:1 for vitamin D to be activated.
This is one of the two fat-soluble vitamins I don’t mind supplementing to reach optimal blood serum levels. Most docs and dietitians like your level of D to be about 30 nmol/L, but an equal number of biohackers and progressive nutritionists prefer that level be bumped up to about 50 nmol/L. That’s difficult to do unless you’re a nudist who lives on a tropical island that mainlines raw tuna. To keep your blood levels up there, use a supplement with microencapsulated vitamin D.
T Nation BiotestI-Well™
400 mg Beta-1,3-Glucan, 400 mg Micellar Curcumin™ Solid Lipid Curcumin Particles, 400 mg EGCG 125 mcg (5000 IU) Microencapsulated Vitamin D3 – 90 Vegetable Capsules

Regarding Vitamin K
This vitamin needs all the fat it can get. That means lots of full-fat salad dressing on your spinach or other vitamin K-rich food. However, like vitamin D, this is another fat-soluble vitamin I’d prefer you supplement. Take it with the fattiest meal of the day, which for most people is dinner. This is a good one.
Regarding Vitamin E
This vitamin only needs a little fat to be absorbed (about 3 grams), but it should be a fat with a higher ratio of unsaturated to saturated fat like grapeseed, sunflower, or safflower. However, ingesting too many of these oils can cause inflammation, which depletes vitamin E stores.
Tell you what, forget all that. Vitamin E needs so little fat in general, just eat your legumes, almonds, butter, or leafy vegetables and don’t worry about it. Avoid supplementing with it, though, as most vitamin E supplements contain astronomical amounts of vitamin E, and that association between vitamin E and cancer, while not conclusively proven, is worrisome.
And to Condense the Recommendations Even Further…
The above synopsis might still have been too lengthy. Tell you what, just try to eat a well-balanced diet and use full-fat dressing on your salads. Don’t supplement with vitamins A or E but consider supplementing with vitamin K.
There. Done.
Youness RA et al. Fat-soluble vitamins: updated review on their role and orchestration in human nutrition throughout life cycle and sex differences. Nutr Metab (Lond). 2022 Sep 5;19(1):60. PubMed.
Jayaran P et al. Effect of dietary fat on absorption of beta carotene from green leafy vegetables in children. Indian J Med Res. 1980 Jan;71:53-6. PubMed.
Roodenburg AJ et al. Amount of fat in the diet affects bioavailability of lutein esters but not of α-carotene, β-carotene, and vitamin E in humans. Am J Clin Nutr. 2000 May;71(5):1187-93. PubMed.
Gijsbers BL et al. Effect of food composition on vitamin K absorption in human volunteers. Br J Nutr. 1996 Aug;76(2):223-9. PubMed.
Niramitmahapanya S et al. Type of Dietary Fat Is Associated with the 25-Hydroxyvitamin D3 Increment in Response to Vitamin D Supplementation. J Clin Endocrinol Metab. 2011 Oct;96(10):3170-4. PubMed.
T Nation earns from qualifying purchases as an Amazon Associate. Read more about our policy.

Download the Slikk Fitness app for iOS for more exclusive content