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.