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Vitamins

Essentials

  • The vitamin requirement of the human body is usually met by adequate nutrition. Due to e.g. environmental factors (especially the exposure to sunlight), diet and some health conditions, specific vitamin deficiencies may anyhow be common in some areas.
    • In northern countries like Finland, vitamin D deficiency is common. In Finland also insufficient intake of thiamine and folate is common.
  • Recommendations concering vitamin intake and supplementation may vary across countries and regions. Always check local recommendations too.
  • Risk groups for vitamin deficiencies include small children, immigrants, people on a vegan diet, elderly with inadequate food intake, alcoholics, and patients suffering from severe systemic diseases. In these groups the prophylactic use of vitamins may be beneficial, and diagnosed vitamin deficiencies should be actively treated.
  • Vegans require vitamin B12 supplementation.
  • All women planning pregnancy and pregnant women (until the end of week 12 of pregnancy) require folic acid supplementation.
  • Consider vitamin deficiency as a possible cause of vague or non-specific symptoms (such as aches, loss of strength, rashes) in the risk groups.

Vitamin D

  • The biologically most active forms of the fat-soluble vitamin D (calcidiol or 25(OH)D or 25-hydroxycholecalciferol) are vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol).
  • Vitamin D3 is synthesized in the skin under the influence of ultraviolet (UV) radiation. Vitamin D2 is acquired in foods of vegetable origin.
  • Recommended supplementation dose varies depending on country and the person's age. Find out about local recommendations. In Finland, the recommended total vitamin D intake in individuals over 75 years of age is 20 µg/day and in others 10 µg/day.
  • Adequate vitamin D concentration may be assessed by determining the concentration of plasma calcidiol. Separate measurements ot D2 and D3 are required only in special cases.
    • <25 nmol/l: severe deficiency
    • <50 nmol/l: deficiency
    • 50-75 nmol/l: generally regarded as adequate concentration
    • 75-120 nmol/l: target concentration in patients with osteoporosis
    • >120 nmol/l: concentration not recommended
    • >375 nmol/l: toxic concentration
  • Risk groups with respect to vitamin D deficiency include newborns and other children, elderly persons, as well as persons living in institutions or who are on vegan diet or have dark skin.
  • Excessive use of vitamin D preparations may lead to vitamin D overdose. Toxic amount of vitamin D cannot be acquired through exposure to sunlight or through diet. Dosage of more than 1 000 µg/day over several months may lead to hypercalcaemia Hypercalcaemia and Hyperparathyroidism and related symptoms.
  • Symptoms of vitamin D poisoning include e.g. loss of appetite, nausea, symptoms of alimentary canal, muscle pain, headache and thirst.

Vitamin D prophylaxisCalcium and Vitamin D for Corticosteroid-Induced Osteoporosis, Vitamin D Supplementation for Prevention of Mortality in Adults, Vitamin D Supplementation for Women during Pregnancy, Vitamin D and Vitamin D Analogues with or Without Calcium Supplement for Preventing Fractures in Post-Menopausal Women and Older Men

  • Sufficient intake of vitamin D is important especially from the viewpoint of the growth and maintenance of bones.
    • Rickets has virtually disappeared in countries where systematic vitamin D prophylaxis for children is practised.
    • Vitamin D belongs to the basic care of osteoporosis Osteoporosis.
  • Vitamin D combined with calcium apparently reduces fractures in people aged over 65 years. Vitamin D may also protect the elderly from falling accidents.
  • Vitamin D (20 µg/day) and calcium supplementation (1 000 mg/day) is important in the prevention of osteoporosis associated with glucocorticoid treatment.
  • In obese people, vitamin D need may be greater than the age group's recommendation.
  • Vitamin D affects the human immune defence by enhancing immunity. Knowledge of the association between vitamin D deficiency and severe pulmonary infection caused by coronavirus has been increasing.
    • Check local recommendations regarding vitamin D supplementation during the COVID-19 pandemic. In Finland, for example, the hospital district responsible for specialized care in the capital region (HUS) recommends vitamin D supplementation to all individuals older than 70 years and special groups during the pandemic.
  • The recommended first-line preparation should contain vitamin D in the form of vitamin D3, which is the natural form for the human body and more effective than vitamin D2.
  • For recommended dosage of vitamin D supplement, see table T1.

Recommended dosage of vitamin D supplement in northern climate

Age groupDaily supplementation in addition to the amount acquired from food, throughout the year
All children less than one year of age, starting at the age of 2 weeks***
  • Fully breastfed child
10 µg (400 IU)/day
  • Child receiving less than 500 ml/day of infant formula/follow-on formula
10 µg (400 IU)/day
  • Child receiving 500-800 ml/day of infant formula/follow-on formula
6 µg (240 IU)/day
  • Child receiving more than 800 ml/day of infant formula/follow-on formula
2 µg (80 IU)/day
Age 1 year10 µg (400 IU)/day
Age 2-17 years7.5 µg (300 IU)/day
Age 18-74 years10 µg (400 IU)/day, only as required *
Age over 7520 µg (800 IU)/day **
Pregnant or breast-feeding women10 µg (400 IU)/day
Recommended total intake (combined amount of vitamin D acquired from food and possible supplementation preparations) is 20 µg/day in individuals over 75 years of age and 10 µg/day in all others.
* During the darkest period of the year (October - March) in the absence of daily consumption of vitamin D-enriched dairy products, dietary fats, and/or fish.
** A smaller supplemental vitamin D dose (10 µg/day) may be sufficient, if diet regularly contains abundant amounts of vitamin D-enriched milk products, dietary fats and/or fish.
*** In infants, a drop preparation is primarily recommended to guarantee reliable dosage. Sprays etc. are not recommended because of their uncertain dosage.

Natural sources of vitamin D

  • In northern countries like Finland, efficient sunlight is provided from April to September only. Therefore, vitamin D acquired through food plays an important role for the well-being of the body. The body requires in total 40 μg of vitamin D per day (from food or food supplements) in order to prevent the concentration of vitamin 25(OH)D from decreasing.
  • The most important dietary sources of vitamin D include vitamin-enriched milk products and edible fat spreads as well as fish. Strict vegan diet that contains absolutely nothing of animal origin, not even dairy products, predisposes to vitamin D deficiency. Some vegetables and mushrooms, however, contain vitamin D.
  • Species of fish rich in fat (salmon, powan, vendace) have traditionally been recommended, but also species with less fat contain vitamin D. Egg yolk, liver, broiler as well as chantarelles and yellowfoot mushrooms are good sources of vitamin D.

Adding vitamin D in food

  • In certain countries, like in Finland, vitamin D3 may be added to all liquid milk products (1-2 µg/100 ml) and all spreads.
  • Not even an abundant use of vitamin-enriched milk products will lead to exceeding of the upper limit of the daily vitamin D intake that is considered safe (children from 0 to 6 months of age 25 μg/day, from 6 to 12 months 35 μg/day, from 1 to 11 years 50 μg/day, and adolescents [from 11 years onwards] and adults 100 µg/day).

Vitamins A and E

  • Vitamins A and E are fat-soluble vitamins.
  • Vitamin A is needed e.g. for maintaining normal eyesight, growth of skin and the skeletal system, function of the immune system and as an antioxidant. Vitamin E acts in the body as an antioxidant.
  • Vitamin A is acquired from food, including both meat and vegetable dishes. Liver is especially rich in vitamin A. Of vegetables, carrots and kale contain lots of beta carotene, a precursor of vitamin A.
  • Reduced vision in low light is often the first symptom of vitamin A deficiency. Drying and irreversible keratinization of the cornea occur in a more severe deficiency. Primary vitamin A deficiency is a rare cause of blindness in industrialized countries but the most common cause in developing countries.
  • Vitamin E deficiency causes neurological symptoms, such as ataxia and peripheral neuropathy, as well as haemolytic anaemia. Vitamin E deficiency is very rare.
  • Disturbances in fat absorption in the intestinal tract (e.g. in patients who have undergone small bowel resection) predispose to deficiency of fat-soluble vitamins A and E.
  • Increased concentrations suggest excessive use of vitamin products.
  • During pregnancy, or when planning one, consumption of large amounts of foods and products containing liver should be avoided.
  • Vitamin A and E concentrations can be assessed by determining respective serum concentrations.

Thiamine (vitamin B1)

  • Thiamine is needed in carbohydrate metabolism.
  • Almost all nutritients, with the exception of sugars and dietary fats, contain thiamine. Foods rich in thiamine include, for example, whole grain foods, meat, fish, poultry, eggs, many vegetables and legumes.
  • A completely thiamine-free diet may cause deficiency symptoms already within a few weeks.
  • Alcoholics are a major risk group in developed countries. The risk of thiamine deficiency is increased also by illnesses causing malabsorption and vomiting, by quick reduction of body weight and by failure to eat.
  • In developing countries, a known thiamine deficiency condition is beriberi, the first symptoms of which include lack of appetite, nausea, heart palpitation, muscular tenderness and difficulties in walking. In alcoholics, the deficiency is often manifested as Wernicke's encephalopathy, see Neurological Disorders and Alcohol.
  • If thiamine deficiency is suspected, the patient is given 250 mg (5 ml) of thiamine through intramuscular injection or slow infusion once daily for a period of 3-5 days.
  • Concentration may be assessed by determining blood thiamine level.

Vitamin B12

  • Vitamin B12 consists of a group of cobalamins that act as coenzymes. Vitamin B12 has a role in the metabolism of amino acids and nucleic acids by converting folate to biologically active form.
  • Vitamin B12 is only acquired from food of animal origin, e.g. liver and milk products. Vegan diet does not provide a sufficient amount of vitamin B12.
  • In order for vitamin B12 to be absorbed it must first be bound to the intrinsic factor, which is secreted by the gastric wall. Low concentrations of intrinsic factor occur e.g. in atrophic gastritis, coeliac disease, Crohn's disease, broad (fish) tapeworm disease Tapeworm Disease and following bariatric surgery. Some drugs (metformin, for example) may impair absorption of vitamin B12.
  • B12 vitamin concentration may be assessed by determining the biologically active transcobalamin-bound vitamin B12.
  • Symptoms of vitamin B12 deficiency include megaloblastic anaemia, exhaustion, various neurological disturbances as well as glossitis.
  • Vitamin B12 is a safe vitamin, since toxic effects have not been observed even when the intake is high.
  • Vitamin B12 should be given to patients with established deficiency or a clear risk of developing one. For more detailed information on investigations and treatment of vitamin B12 deficiency, see Megaloblastic Anaemia.

Folate and folic acid

  • Folate is a water-soluble vitamin in the vitamin B group, needed for the metabolism of amino acids and nucleic acids. The conversion of folate to biologically active form requires vitamin B12.
  • Folate is the name for the natural form present in food. Folic acid is the respective synthetic vitamin present in vitamin preparations, dietary supplements and supplemented foods.
  • Folate is found abundantly e.g. in whole grain cereals, potatoes, green vegetables and liver.
  • Folate deficiency may be caused by too low intake (inadequate diet or malabsorption, e.g. coeliac disease) or increased need e.g. during pregnancy. Deficiency may also be caused by several different pharmaceuticals (e.g. methotrexate, some antiepileptics).
  • Symptoms of folate deficiency include megaloblastic anaemia, alterations in the skin, loss of appetite, muscular weakness, intestinal symptoms, reduced growth and neurological symptoms.
  • Folate concentration can be assessed by determination of serum folate.
  • A daily folic acid dose of 0.4 mg is recommended to all women planning pregnancy and to all pregnant women (until the end of week 12 of pregnancy) to prevent neural tube defects. Special groups require a higher dose, see Antenatal Clinics: Care and Examinations and local recommendations.
  • High intake of folic acid may mask vitamin B12 deficiency. Oral folic acid supplementation of more than 1 mg/day should not be started to treat macrocytic anaemia in a patient, even if his/her folate concentration would be low, before an underlying B12 deficiency has been excluded.
  • Folic acid should be given to patients with established deficiency or a clear risk of developing one. For more detailed information on investigations and treatment of folate deficiency, see Megaloblastic Anaemia.

Vitamin C Vitamin C for Pneumonia, Vitamin C Supplementation for Asthma, Vitamin C for Treating Tetanus, Vitamin C Supplementation in Pregnancy, Vitamin C for Preventing and Treating the Common Cold

  • Vitamin C (L-ascorbate or L-ascorbic acid) is an antioxidant that functions as cofactor of enzymatic reactions and enhances iron absorption.
  • Dietary sources include fruits (especially citrus fruits), berries, vegetables and potatoes.
  • Recommended vitamin C intake varies. In Finland, for example, it is 75 mg/day.Check local recommendation.
  • Risk groups of vitamin C deficiency include persons with very monotonic diet (alcoholics, chronically ill persons, elderly persons)
  • Deficiency is manifested as the disease scurvy which starts developing after 1-3 months of vitamin C deficiency. First symptoms include various haemorrhages and fatigue.
  • The absorption of vitamin C is reduced when consumption is high. A high single dose (over 3 g) may cause gastrointestinal symptoms, such as diarrhoea and gas buildup. High doses of vitamin C may be harmful to persons inclined to developing urinary calcium oxalate calculi.

Vitamin K Vitamin K for Improved Anticoagulation Control in Patients Receiving Warfarin

  • Fat-soluble K-vitamins affect mainly blood coagulation and calcium metabolism, as well as the health of the skeleton and blood vessels.
  • Vitamin K1 (phylloquinone) is of vegetable origin and K2 vitamins (menaquinones) are produced by microbes.
  • In the EU, sufficient intake in adults has been estimated to be 70 µg/day. The most important sources include vegetables and vegetarian food, meat and egg food as well as cereal products.
  • Vitamin K deficiency manifests itself as longer blood coagulation time, bleeding and anaemia. The condition is very rare in adults and is caused mainly by fat malabsorption (e.g. liver diseases, untreated coeliac disease).
  • Newborns are given 1 mg of vitamin K intramuscularly to reduce bleeding risk.
  • Vitamin K is used in adults for the treatment of warfarin overdose. Regular use of green vegetables or a minor vitamin K1 supplementation may even out fluctuation of INR levels and improve the control of warfarin therapy. See warfarin therapy Warfarin Therapy.

Evidence Summaries ⬆