The biochemical functions of most vitamins have been well studied. Generally speaking, vitamins are the main or only component of coenzyme. Coenzyme can be regarded as a part of the enzyme complex that promotes biochemical reactions. Only when enzyme and coenzyme exist at the same time can the biochemical reaction proceed normally.
It is generally believed that a normal diet should include enough five basic ingredients: cereals, meat, dairy products, vegetables and fruits to supplement enough vitamins and trace elements.
The important question is how many people can reach the ideal diet standard.
The current situation is far from meeting the requirements of RDA (Recommended Daily Allowance).
Moreover, with the popularity of fast food and the development of so-called "healthy diet", it is increasingly difficult to meet the prescribed vitamin intake standards by strictly controlling calories.
Although Frank's vitamin deficiency is rare in developed countries (such as the United States), there may still be many groups who cannot get enough vitamin nutrition because of diet or other factors.
Vitamins A, D, E and K are all fat-soluble vitamins, which are related to the absorption of lipids. Therefore, any state that weakens fat absorption can affect the absorption of fat-soluble vitamins. Cholestasis, cholecystitis, inflammatory diarrhea and other diseases may lead to fat-soluble vitamin deficiency.
Similarly, drugs and mineral oil that affect fat absorption may also lead to fat-soluble vitamin deficiency.