The Fat-Soluble Vitamins: A, D, E and K

		RDA (IU / mcg)	UL (IU / mcg)
Infants	0–6 months	1,333 / 400	2,000 / 600
	7–12 months	1,667 / 500	2,000 / 600
Children	1–3 years	1,000 / 300	2,000 / 600
	4–8 years	1,333 / 400	3,000 / 900
	9–13 years	2,000 / 600	5,667 / 1700
Women	14–18 years	2,333 / 700	9,333 / 2800
	19–70 years	2,333 / 700	10,000 / 3000
Men	14–18 years	3,000 / 900	9,333 / 2800
	19–70 years	3,000 / 900	10,000 / 3000

Summary:

The RDA for vitamin A is 3,000 IU (900 mcg) for adult men and 2,333 (700 mcg) for women. For children, it ranges from 1,000 IU (300 mcg) to 2,000 IU (600 mcg).

Vitamin A Deficiency

Vitamin A deficiency is rare in developed countries.

However, vegans may be at risk, since pre-formed vitamin A is only found in animal-sourced foods.

Although provitamin A is abundant in many fruits and vegetables, it is not always efficiently converted into retinol, the active form of vitamin A. The efficiency of this conversion depends on people’s genetics (12, 13).

Deficiency is also widespread in some developing countries where food variety is limited. It is common in populations whose diet is dominated by refined rice, white potatoes or cassava and lacking in meat, fat and vegetables.

A common symptom of early deficiency includes night blindness. As it progresses, it may lead to more serious conditions, such as:

• Dry eyes: Severe deficiency may cause xerophthalmia, a condition characterized by dry eyes caused by reduced tear fluid formation (2).
• Blindness: Serious vitamin A deficiency may lead to total blindness. In fact, it is among the most common preventable causes of blindness in the world (14).
• Hair loss: If you are vitamin A deficient, you may start to lose your hair (15).
• Skin problems: Deficiency leads to a skin condition known as hyperkeratosis or goose flesh (16).
• Poor immune function: Poor vitamin A status or deficiency makes people prone to infections (3).

Summary:

Severe vitamin A deficiency may lead to blindness. Other symptoms may include hair loss, skin problems and an increased risk of infections.

Vitamin A Toxicity

Overdosing on vitamin A leads to an adverse condition known as hypervitaminosis A. It’s rare, but may have serious health effects.

Its main causes are excessive doses of vitamin A from supplements, liver or fish liver oil. In contrast, high intake of provitamin A does not cause hypervitaminosis.

The main symptoms and consequences of toxicity include fatigue, headache, irritability, stomach pain, joint pain, lack of appetite, vomiting, blurred vision, skin problems and inflammation in the mouth and eyes.

It may also lead to liver damage, bone loss and hair loss. At extremely high doses, vitamin A can be fatal (17).

People are advised to avoid exceeding the upper limit for intake, which is 10,000 IU (900 mcg) per day for adults.

Higher amounts, or 300,000 IU (900 mg), may cause acute hypervitaminosis A in adults. Children can experience harmful effects at much lower amounts (18).

Individual tolerance varies considerably. Children and people with liver diseases like cirrhosis and hepatitis are at an increased risk and need to take extra care.

Pregnant women should also be especially careful, since high doses of vitamin A may harm the fetus. Doses as low as 25,000 IU per day have been linked with birth defects (19).

Summary:

High doses of vitamin A may lead to hypervitaminosis A, which is associated with various symptoms. Pregnant women should avoid eating high amounts of vitamin A because of the risk of birth defects.

Benefits of Vitamin A Supplements

While supplements are beneficial for those who suffer from deficiency, most people get enough vitamin A from their diet and do not need to take supplements.

Yet, controlled studies suggest that vitamin A supplements may benefit certain people even if their diet meets the basic requirements.

For instance, vitamin A supplements may help treat measles in children (20, 21).

They protect against measles-associated pneumonia and reduce the risk of death by 50–80%. Studies suggest that vitamin A acts by suppressing the measles virus (22).

Summary:

Supplements mainly benefit those who are low or deficient in vitamin A. One exception is children with measles, as studies show that supplements may help treat the disease.

Summary of Vitamin A

Vitamin A, also known as retinol, is a fat-soluble vitamin traditionally associated with vision and eye health.

The most abundant dietary sources of vitamin A are liver, fish liver oil and butter.

It can also be derived from provitamin A carotenoids found in red, yellow and orange vegetables, as well as some leafy, dark-green vegetables.

Deficiency is rare in developed countries, but is most common among people who follow diets lacking in diversity, especially those dominated by rice, white potatoes and cassava.

Early symptoms of vitamin A deficiency include night blindness, and severe deficiency may eventually lead to total blindness.

Nevertheless, while getting enough vitamin A is vital, too much may cause harm.

Pregnant women should be extra careful not to eat excessive amounts of vitamin A because of the risk of birth defects.

Age Group	RDA (IU / mcg)	UL (IU / mcg)
0–6 months	400 / 10*	1,000 / 25
7–12 months	400 / 10*	1,500 / 38
1–3 years	600 / 15	2,500 / 63
4–8 years	600 / 15	3,000 / 75
9–70 years	600 / 15	4,000 / 100
70+ years	800 / 20	4,000 / 100

If you want to find out more about the optimal intake of vitamin D, read this article.

Summary:

For children and adults, the RDA for vitamin D is 600 IU (15 mcg). The amount is slightly higher for elderly adults, at 800 IU (20 mcg).

Vitamin D Deficiency

Severe vitamin D deficiency is rare, but mild forms of deficiency or insufficiency are common among hospitalized people as well as the elderly.

Risk factors of deficiency are dark skin color, old age, obesity, low sun exposure and diseases that impair fat absorption.

The most well-known consequences of vitamin D deficiency include soft bones, weak muscles and an increased risk of bone fractures. This condition is called osteomalacia in adults and rickets in children (28).

Vitamin D deficiency is also associated with poor immune function, an increased susceptibility to infections and autoimmune diseases (29, 30).

Other signs of deficiency or insufficiency may include fatigue, depression, hair loss and impaired wound healing.

Observational studies have also linked low vitamin D levels or deficiency with an increased risk of dying from cancer and an elevated risk of heart attacks (31, 32).

Summary:

The main symptoms of vitamin D deficiency include fatigue, weak muscles, soft bones, an increased risk of fractures and susceptibility to infections.

Vitamin D Toxicity

Vitamin D toxicity is very rare.

While spending a lot of time in the sun doesn’t cause vitamin D toxicity, taking high amounts of supplements may harm you.

The main consequence of toxicity is hypercalcemia, a condition characterized by excessive amounts of calcium in the blood.

Symptoms include headache, nausea, lack of appetite, weight loss, fatigue, kidney and heart damage, high blood pressure and fetal abnormalities, to name a few.

People are generally advised to avoid exceeding the upper limit of vitamin D intake, which is 4,000 IU per day for adults.

Higher amounts, ranging from 40,000–100,000 IU (1,000–2,500 mcg) per day, may cause symptoms of toxicity in adults when taken daily for one or two months. Keep in mind that much lower doses may harm young children.

To learn more about how much vitamin D you can safely take, read this article.

Summary:

Vitamin D is toxic in high doses. The most serious symptoms are caused by dangerously high levels of calcium in blood, which may harm the heart and kidneys.

Benefits of Vitamin D Supplements

For people who spend little time in the sun and seldom eat fatty fish or liver, supplements can be very beneficial.

Regularly taking supplements seems to prolong people’s lives, especially hospitalized or institutionalized elderly people (33, 34).

Supplements may also reduce the risk of respiratory tract infections (35, 36).

They may also have many other benefits in people with vitamin D deficiency, but more studies need to examine their effects in people with sufficient vitamin D levels.

Summary:

Health professionals advise most people to take vitamin D supplements to prevent deficiency. Supplements may improve general health and reduce the risk of infections.

Summary of Vitamin D

Vitamin D is sometimes called the sunshine vitamin. This is because your skin can produce all the vitamin D you need, given enough sunlight.

Nevertheless, most people don’t get enough vitamin D from sunlight alone. Also, few foods naturally contain high amounts of vitamin D, making supplements necessary.

The richest natural sources of vitamin D include fatty fish, fish oil and mushrooms that have been exposed to sunlight or ultraviolet light.

Vitamin D deficiency is traditionally associated with osteomalacia in adults, or rickets in children. Both diseases are characterized by brittle or soft bones.

		RDA (IU / mg)	UL (IU / mg)
Infants	0–6 months	6 / 4*	Not known
	7–12 months	8 / 5*	Not known
Children	1–3 years	9 / 6	300 / 200
	4–8 years	11 / 7	450 / 300
	9–13 years	17 / 11	900 / 600
Adolescents	14–18 years	23 / 15	1,200 / 800
Adults	19–50 years	23 / 15	1,500 / 1,000
	51+	18 / 12	1,500 / 1,000

Summary:

Among adults, the RDA for vitamin E is 23 IU (15 mg). For children and adolescents, the RDA ranges from 9 IU (6 mg) to 23 IU (15 mg), depending on the age group.

Vitamin E Deficiency

Vitamin E deficiency is uncommon and is never detected in people who are otherwise healthy.

It happens most often in diseases that impair the absorption of fat or vitamin E from food, such as cystic fibrosis and liver disease.

Symptoms of vitamin E deficiency include muscle weakness, walking difficulties, tremors, vision problems, poor immune function and numbness.

Severe, long-term deficiency may lead to anemia, heart disease, serious neurological problems, blindness, dementia, poor reflexes and the inability to fully control body movements (39, 40).

Summary:

Vitamin E deficiency is rare, but can cause muscle weakness, susceptibility to infections, neurological problems and poor vision.

Vitamin E Toxicity

Overdosing on vitamin E is difficult when it is obtained from natural dietary sources. Cases of toxicity have only been reported after people have taken very high doses of supplements.

Yet, compared to vitamin A and D, overdosing on vitamin E appears to be relatively harmless.

It may have blood-thinning effects, counteracting the effects of vitamin K and causing excessive bleeding. Thus, people who take blood-thinning medications should avoid taking large doses of vitamin E (38, 41, 42).

Additionally, at high doses of more than 1,000 mg per day, vitamin E may have pro-oxidant effects. That is, it can become the opposite of an antioxidant, potentially leading to oxidative stress (43).

Summary:

Vitamin E appears to be less toxic at high doses than vitamin A and D. However, high doses may cause excessive bleeding and oxidative stress.

Benefits and Risks of High Vitamin E Intake or Supplements

High vitamin E intake from food or supplements has been linked with a number of benefits.

One form of vitamin E, gamma-tocopherol, was found to increase blood flow by promoting the dilation of blood vessels, potentially reducing blood pressure and the risk of heart disease (44).

Gamma-tocopherol supplements may also have a blood-thinning effect as well as reducing levels of “bad” LDL cholesterol (45).

In contrast, other studies suggest that high-dose vitamin E supplements may be harmful, even when they don’t cause any obvious symptoms of toxicity.

For instance, observational studies show that taking vitamin E supplements is linked with an increased risk of prostate cancer and death by all causes (46, 47, 48).

Given the potentially adverse effects of vitamin E supplements, they cannot be recommended at this point. High-quality studies are needed before solid conclusions can be reached about the long-term safety of these supplements.

Summary:

Vitamin E supplements may reduce the risk of heart disease, but the evidence is conflicting. Some studies suggest that high-dose supplements are harmful. More studies are needed.

Summary of Vitamin E

Vitamin E is a group of powerful antioxidants, the most common of which is alpha-tocopherol.

Its main function is to serve as an antioxidant and protect the body’s cells against damage by free radicals.

The most abundant dietary sources of vitamin E include vegetable oils, nuts and seeds. Deficiency is very rare in healthy people.

While supplements may provide certain health benefits, not all scientists agree. The long-term safety of vitamin E supplements is a matter of debate.

		Al (mcg)
Infants	0-6 months	2
	7–12 month	2.5
Children	1–3 years	30
	4–8 years	55
	9–13 years	60
Adolescents	14–18 years	75
Women	18+ years	90
Men	18+ years	120

Summary:

The adequate intake (AI) of vitamin K is 90 mcg for women and 120 mcg for men. For children and adolescents, the AI ranges from 30–75 mcg, depending on the age group.

Vitamin K Deficiency

Unlike vitamins A and D, vitamin K isn’t stored in the body in significant amounts. For this reason, consuming a diet lacking in vitamin K may lead you to become deficient in as little as a week (53).

People who do not efficiently digest and absorb fat are at the greatest risk of developing vitamin K deficiency. This includes those who suffer from celiac disease, inflammatory bowel disease and cystic fibrosis.

Use of broad-spectrum antibiotics may also raise the risk of deficiency, as well as very high doses of vitamin A, which seem to reduce vitamin K absorption.

Mega-doses of vitamin E may also counteract the effects of vitamin K on blood clotting (41, 54).

Without vitamin K, your blood wouldn’t clot and even a small wound could cause unstoppable bleeding. Fortunately, vitamin K deficiency is rare, since the body only needs small amounts to maintain blood clotting.

Low levels of vitamin K have also been linked with reduced bone density and increased risk of fractures in women (55).

Summary:

Deficiency in vitamin K may lead to excessive bleeding. Diseases that interfere with fat absorption increase the risk of deficiency.

Vitamin K Toxicity

Unlike the other fat-soluble vitamins, natural forms of vitamin K have no known symptoms of toxicity.

As a result, scientists have not been able to establish a tolerable upper intake level for vitamin K. Further studies are needed.

In contrast, a synthetic form of vitamin K, known as menadione or vitamin K3, may have some adverse effects when consumed in high amounts (56, 57).

Summary:

The maximum safe dosage of vitamin K is unknown and no symptoms of toxicity have been identified.

Benefits of Vitamin K Supplements

Several controlled studies have examined the effects of vitamin K supplements in humans. These studies show that vitamin K supplements — vitamin K1 and vitamin K2 — may decrease bone loss and reduce the risk of bone fractures (58, 59).

Additionally, taking vitamin K2 supplements at 45–90 mg per day slightly increased the survival of patients with liver cancer (60).

Observational studies also suggest that a high intake of vitamin K2 may lower the risk of heart disease. However, the evidence from controlled studies is limited and inconclusive (61, 62).

Finally, vitamin K1 supplements taken at 0.5 mg every day for three years slowed the development of insulin resistance in older men, compared to a placebo. No significant differences were detected in women (63).

Summary:

Limited evidence suggests that vitamin K supplements may improve bone health, reduce the risk of heart disease and increase survival among liver cancer patients.

Summary of Vitamin K

Vitamin K is a group of fat-soluble compounds divided into vitamin K1 (phylloquinone) and vitamin K2 (menaquinone).

Vitamin K1 is mainly found in leafy green vegetables, whereas vitamin K2 comes from animal-sourced foods, such as liver, butter and egg yolks.

Small amounts are also produced by gut bacteria in the colon.

Deficiency impairs the blood’s ability to clot, causing a risk of excessive bleeding.

There is limited evidence on the health benefits of supplements among people who aren’t deficient. However, a few controlled studies suggest that vitamin K supplements benefit bone and heart health.