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Nutrition Library

Vitamin A

General Information
  • Vitamin A (retinol) is a fat-soluble vitamin and is only found in animal products.
  • Beta-carotene is mainly found in plant-based foods. Beta-carotene is a precursor of vitamin A (provitamin A) and can be converted into vitamin A in the body.
  • Once the body’s stores of vitamin A are full, then additional provitamin A (e.g., beta-carotene) is not converted into the active vitamin. Instead, it remains present in the body as an antioxidant or is excreted by the kidneys.
  • It should be noted that significant amounts of beta-carotene are required to create sufficient vitamin A in the body.
  • The supply of vitamin A is generally unproblematic in countries with stable food security and a large food selection.
  • Vitamin A deficiency mainly affects countries with unstable food security and limited food choices, and above all children.
  • Those eating a purely plant-based (vegan) diet should pay attention to beta-carotene intake, since high intake levels are required for vitamin A formation. The body needs about 12 – 24 mg beta carotene to form 1 mg vitamin A.
  • The absorption of vitamin A can be significantly improved by consuming it with fat.
  • Zinc is essential for vitamin A metabolism.
Why Do We Need Vitamin A?
  • Important for vision
  • Important for growth and differentiation of cells and tissues
  • Health and function of the skin and mucous membranes
  • Normal functioning of the immune system
  • Antioxidant effects
  • Important for the hormone metabolism
  • Childhood growth and development
Possible Causes of Deficiency

Low intake:

  • Diet contains too little vitamin A or beta carotene

Increased demand or consumption:

 

  • Pregnancy, lactation
  • Growth
  • Chronic infections, especially in children
  • Stress
  • Smoking, high alcohol consumption

Reduced absorption:

  • Chronic diarrhea, Crohn’s disease, pancreatitis, celiac disease

Interaction with medications (may impair absorption/utilization):

  • e.g., antacids, antiepileptics, Colchicine, cholestyramine, fat blockers such as orlistat

Zinc deficiency

Symptoms of Deficiency
  • General: loss of appetite, fatigue, susceptibility to infection
  • Eyesight: sensitivity to glare, slow adaptation to light/darkness, night blindness, eye dryness
  • Skin/hair/nails: dry, scaly, wrinkled skin, brittle nails, and hair
  • Immune system: frequent infections (especially respiratory tract)
  • Mucous membranes: dehydration, loss of taste, smell, inflammation of the oral mucosa or gums
Recommended Intakes

 

In order to list together different sources of vitamin A (as retinol from animal products) and provitamin A (especially beta-carotene from plant products) in food, the vitamin A requirement is stated in retinol equivalents (RA). This represents the sum of intake from both sources. The body needs about 6 times the amount of provitamin A to form vitamin A – or, according to some recent studies, perhaps even 12-24 times as much.

  • 1mg retinol equivalent = 1mg vitamin A (retinol)
  • 1mg retinol equivalent = 6mg provitamin A (beta-carotene)

1000µ = 1mg

Recommended intake for adults:

  • according to D-A-CH: women 800 µg/day, men 1000 µg/day,
  • USA Food and Nutrition Board (FNB): women 700 µg/day, men 900 µg/day

Pregnant women:

  • According to D-A-CH: 1100 µg/day
  • USA Food and Nutrition Board (FNB): 770 µg/day
  • Due to teratogenic risk, pregnant women should not take vitamin A without medical supervision!

Breastfeeding women:

  • according to D-A-CH: 1500 µg/day
  • USA Food and Nutrition Board (FNB): 1300 µg/day

In children and adolescents depending on age, see

 

  • The beta-carotene present in plant foods, which is a precursor of vitamin A, is not toxic even in high doses. However, excessive intake can lead to yellowing of the skin.
  • Vitamin A itself can, in very high doses, lead to toxic damage. Symptoms include loss of appetite, headache, hair loss, flaky, dry skin, bone pain, or liver damage. The highest safe dose (UL) is 3000 µg/day.
The Best Plant Sources (per 100 g)

Beta carotene is mainly found in yellow or red fruits and vegetables.

Important to know: The bioavailability of beta-carotene differs depending on food preparation method. For example, the beta carotene in carrots is absorbed well only when carrots are cooked or juiced.

  • Apricot, dried – 5800µg
  • Carrots – 1700 µg
  • Kale, raw – 1445 µg
  • Sweet potato, raw – 1300 µg
  • Dandelion leaves – 1300 µg
  • Pumpkin, raw – 830 µg
  • Watercress – 820 µg
  • Rose hips – 800 µg
  • Fennel – 780 µg
  • Savoy cabbage, raw – 780 µg
  • Honeydew melon – 780µg
  • Corn salad – 660 µg
  • Swiss chard – 590 µg
  • Chicory – 570 µg
  • Spinach – 550 µg
  • Romaine lettuce – 435 µg
  • Dill, fresh – 385 µg
  • Parsley, fresh – 385 µg
  • Garden cress, raw – 365 µg
  • Arugula – 230 µg
  • Mango – 205µg
  • Tomato paste – 200 µg
  • Paprika – 180 µg
  • Papaya – 160µg
  • Tomato juice – 150 µg
  • Tomatoes – 114 µg
  • Apricots, raw – 135 µg
  • Grapefruit – 98 µg
  • Nectarine – 70 µg
  • Elderberries, raw, black – 60 µg
  • Broccoli, raw – 50 µg
  • Green beans – 50µ

 

Sources
  • Gröber, U. (2011): Mikronährstoffe. Metabolic Tuning – Prävention – Therapie (3. Auflage). Wissenschaftliche Verlagsgesellschaft mbH Stuttgart
  • Biesalski, H.K., Bischoff, S.C., Pirlich, M., Weidmann, A., (2018). Ernährungsmedizin – Nach dem Curriculum Ernährungsmedizin der Bundesärztekammer (5.Auflage). Stuttgart: Georg Thieme Verlag
  • Schmiedel, V. (2019): Nährstofftherapie – Orthomolekulare Medizin in Prävention, Diagnostik und Therapie (3.Auflage). Stuttgart: Georg Thieme Verlag