Vitamins can be classified based on their solubility.

Most are water-soluble, meaning they dissolve in water. In contrast, the fat-soluble vitamins are similar to oil and do not dissolve in water.

Fat-soluble vitamins are most abundant in high fat foods and are much better absorbed into your bloodstream when you eat them with fat.

There are four fat-soluble vitamins in the human diet:

  • vitamin A
  • vitamin D
  • vitamin E
  • vitamin K

This article provides a comprehensive overview of the fat-soluble vitamins that includes:

  • health benefits
  • functions
  • main dietary sources

Vitamin A

Vitamin A plays a key role in maintaining your vision. Without it, you would go blind.


Vitamin A is not a single compound. Rather, it is a group of fat-soluble compounds collectively known as retinoids.

The most common dietary form of vitamin A is retinol. Other forms — retinal and retinoic acid — are found in the body, but absent or rare in foods.

Vitamin A2 (3,4-dehydroretinal) is an alternative, less active form found in freshwater fish (1Trusted Source).

Role and function of vitamin A

Vitamin A supports many critical aspects of your body function, including:

  • Vision maintenance. Vitamin A is essential for maintaining the light-sensing cells in your eyes and for the formation of tear fluid (2Trusted Source).
  • Immune function. Vitamin A deficiency impairs your immune function, increasing susceptibility to infections (3Trusted Source4Trusted Source).
  • Body growth. Vitamin A is necessary for cell growth in your body. Deficiency may slow or prevent growth in children (5Trusted Source).
  • Hair growth. It is also vital for hair growth. Deficiency leads to alopecia, or hair loss (6Trusted Source).
  • Reproductive function. Vitamin A maintains fertility and is vital for fetal development