Vitamin A

• Levels are affected by preexisting conditions such as abetalipoproteinaemia, carcinoid syndrome, chronic infections, cystic fibrosis, disseminated tuberculosis, hypothyroidism,¹ liver disease or a systemic inflammatory response,² as well as diseases that cause fat malabsorption, including impaired pancreatic and/or biliary secretions such as Crohn’s and coeliac disease, radiation enteritis, ileal resection or damage.³

• Zinc deficiency impairs the absorption, transport and metabolism of vitamin A.⁴

• Protein deficiency can markedly affect vitamin A nutriture and in turn vitamin A deficiency can also influence protein metabolism.⁵

• Preterm infants are generally considered to be at risk because their plasma retinol concentrations are usually low.⁶

Vitamin B1

• Levels are affected by chronic alcoholism, gastric bypass surgery and gastrointestinal disorders.⁷

• Thiaminases that degrade thiamine are present in raw fish, fish paste and betel nut.⁷

• Antithiamine factors are also found in caffeic acid, tannic acid and salicylic acid, as well as blueberries, black currants, red cabbage, beetroot and brussels sprouts.⁸

Vitamin B2

• Levels are affected by alcoholism,⁹ diabetes mellitus, thyroid and adrenal insufficiency, liver disease, and gastrointestinal or biliary obstruction.¹⁰

• Several metals form chelates or complexes that may affect their bioavailability, such as copper, zinc, iron, tryptophan and vitamins B3 and C, as well as caffeine and saccharin.¹¹

• Protein–energy malnutrition leads to increased urinary losses.¹²

• Exercise increases requirements.¹²

Vitamin B3

• Alcoholism, Crohn’s disease and anorexia ¹²

Vitamin B6

• Levels are affected by alcoholism, asthma, carpal tunnel syndrome, gestational diabetes, lactation, malabsorption, malnutrition, neonatal seizures, normal pregnancies, occupational exposure to hydrazine compounds, pellagra, preeclamptic oedema, renal dialysis, uraemia,¹ liver disease, oestrogen therapy, rheumatoid arthritis and HIV.¹³

• Vitamin B6 antagonists exist in foods such as some varieties of mushrooms, flaxseed meal, jack beans and mimosa, possibly via a systemic effect rather than interfering with its absorption.¹⁴

• Levels are affected by vitamin B2 deficiency.¹⁵

Vitamin B12

• Inadequate peptic digestion and gastric acid,¹⁶ pancreatic insufficiency³ and alcoholism may result in deficiency due to inadequate ingestion and absorption, as well as enhanced utilisation and excretion.¹⁷

• Bacterial overgrowth,¹⁸ tropical or non-tropical sprue, Crohn’s disease and inflammatory bowel disease may cause decreased levels.¹

• Absorption through receptor sites in the ileum occurs in alkaline pH in the presence of calcium.¹⁰

• Diabetes, leukocytosis, hepatitis, cirrhosis, obesity and protein–energy malnutrition may cause increased levels.¹

Folate

• Hyperthyroidism, pregnancy, haemolytic anaemia, the need for intensive care or any other sustained metabolic drain may increase folate need up to six- to eightfold.¹⁹

• Malabsorption of folate occurs secondary to an infection with Giardia lamblia and bacterial overgrowth.¹⁰

• Achlorhydria, oral contraceptive agents,¹⁴ oral oestrogen and antacids affect folate levels.²⁰

• Conditions of increased cellular turnover such as cancer affect folate levels.¹⁰

• Vitamin B12 deficiency may induce a secondary folate deficiency by reducing the activity of the enzyme methionine synthase, which activates folate.¹⁰

Biotin

• Achlorhydria and alcoholism affect biotin levels.²¹

• Biotinases that degrade biotin are found in the protein avidin in raw egg white.²¹

Vitamin C

• Levels are affected by alcoholism, anaemia, cancer, haemodialysis, hyperthyroidism, malabsorption, rheumatoid disease ¹ and oral contraceptive pills, while acute infection and stress may increase urinary excretion.¹⁰

• Deficiency can occur secondary to some disease states such as liver disease, cancer, gastrointestinal disorders, cigarette smoking and environmental exposure.¹⁰

• Aspirin usage affects levels.²²

• Excess iron and copper affect levels.¹⁴

• Pregnancy also lowers serum levels due to haemodilution and active transfer to the fetus, especially during the last trimester.¹⁰

Vitamin E

• Fat malabsorption syndromes such as coeliac disease, cystic fibrosis and chronic cholestatic liver disease ²³, chronic pancreatitis, pancreatic carcinoma, chronic cholestasis,¹ gastric surgery and alcoholism affect levels.¹²

• Levels are affected by abetalipoproteinaemia (which involves a defect in chylomicron synthesis), hyperthyroidism, cirrhosis of the liver, hereditary spherocytosis and β-thalassaemia, as well as associated with conditions such as bronchopulmonary dysplasia and retrolental fibroplasia.²⁴

• Those with protein energy malnutrition ²⁵ and premature²⁶ and low birth weight infants²⁷ and children with cystic fibrosis are often found to have a vitamin E deficiency, which may also occur in children with chronic cholestasis.²⁸

• Obstructive liver disease may increase levels.¹