Topic 3 Fat-soluble vitamins

  • Fat-soluble protect cell membranes from free radical damage. They also influence gene expression and can modify the cell’s nucleus.
  • Fat soluble vitamins can be stored in large quantities
  • This poses a risk as evidence of fat-soluble vitamin deficiency or toxicity may not be immediately evident as it may take some time for the consequences to appear.
  • There are 4 types of fat-soluble vitamins, namely A, D, E, K.

Vitamin A

  • Vitamin A has two main forms obtained from food: retinol or retinyl esters and provitamin A (beta-carotene)
    • Carrots, mangoes, papaya, green leafy vegetables, and fish oil are the main sources
  • Vitamin A may reduce lung cancer risk as well as prostate cancer and age-related vision disease risk.
  • Vitamin A toxicity is more likely to occur in developed countries where high Vit. A doses are found in supplements.
    • No more than 3000 μg should be consumed daily
    • Vitamin A toxicity can induce vision changes (e.g. blurry vision), bone pain, nausea, vomiting and sensitivity to bright light.
    • Toxicity is especially harmful for pregnant women, so food sources very high in Vitamin A should be avoided (liver, liver products, enriched foods)

Vitamin D

  • Vitamin D is well known for its relationship to sunlight but is also found in fatty fish, egg yolks, and beef liver
    • Daily RDA is 15 μg
  • Vitamin D can prevent poor bone health in later age, many types of cancer, cardiovascular diseases, type 2 diabetes
  • Vitamin D deficiency is common in areas where sunlight is limited like the north and south pole.
    • For those living in such regions or during the winter, it is recommended that vitamin D supplements be taken
    • Food can provide some vitamin D but is less effective than sun exposure.

Vitamin E

  • Vitamin E is an antioxidant which can reduce cardiovascular disease and cancer risk
  • Vitamin E can also help prevent poor cognitive function in later age
  • Vitamin E is found in vegetable oils (olive, sunflower, soybean), nuts, avocado and 15 mg should be consumed daily
  • Due to its presence in foods and supplements, deficiency is rare. Toxicity is also rare.

Vitamin K

  • Vitamin K has two forms: K1 (phylloquinone) and K2 (menadione).
  • Vitamin K1 is mostly found in leafy green vegetables and 120 μg should be consumed daily
  • Vitamin K2 is produced by bacteria (fermented products, or own large intestine)
  • Vitamin K helps blood clot and is therefore related to cardiovascular health
  • Deficiency may result in blood loss as clotting ability is decreased
  • People who take medication to affect blood clotting should monitor their vitamin K intake.