Vitamin basics
General guides to vitamins: what they are, fat- and water-soluble types, deficiency symptoms, timing, multivitamins, pregnancy and children.
These guides are about vitamins as a whole rather than one compound: what vitamins are and which 13 count, why fat-soluble and water-soluble vitamins behave differently, when and with what to take them, and which symptom points to which deficiency.
They set the frame before you read a single-vitamin page. The multivitamin question is answered with PHS II, COSMOS and USPSTF 2022 data; vitamins in children and pregnancy are discussed with national programmes and NICE and WHO guidance.
Each guide states the claim, the population studied and the limits of the evidence. Marketing phrases such as “boosts energy” or “strengthens immunity” are assessed by asking in whom and in which study the effect was measured. The guides are linked: reading the general frame first and then moving to the main guide and sub-guides of the vitamin you care about is the shortest path without reading the same thing twice.
Fat- and water-soluble vitamins
Vitamins A, D, E, and K are fat-soluble; the B vitamins and vitamin C are water-soluble. Solubility affects how a vitamin is absorbed, how much is stored, and how quickly deficiency develops; it does not determine the safety of excess intake on its own.
Is a multivitamin necessary?
- Multiple nutrients: Contributes to daily intake by providing vitamins and minerals in the same product.
- Gaps in diet: Can supplement inadequate intake of the nutrients it contains; which functions it supports depends on its content.
Types of vitamins
The thirteen vitamins are divided into two groups: fat-soluble (A, D, E, K) and water-soluble (C and eight B vitamins). Each vitamin has a different function, food sources, deficiency disease, and upper limit; the table below shows them all together.
Deficiency symptoms
Vitamin deficiency symptoms are mostly complaints such as fatigue, hair loss, numbness, or cramps that also occur with many other causes. The findings of overt deficiency diseases (such as scurvy, night blindness, and rickets) are specific to vitamins; in mild deficiencies, diagnosis is made with a blood test.
Vitamins for children
Routine vitamin practices in children are limited: in Türkiye, Ministry of Health programs give infants vitamin D, plus iron support between 4 and 12 months. According to one review, even in picky eaters intake is generally above recommended values; upper limits for children are lower than for adults.
Vitamins in pregnancy
In pregnancy, the requirement for some nutrients such as folate, iron, iodine, and vitamin D increases, and guidelines describe physician-directed supplement programs for this. High amounts of preformed vitamin A, however, are associated with birth defects and are avoided in pregnancy.
What are vitamins?
Vitamins are organic substances needed in small amounts for the body's functions such as growth, energy metabolism, blood production, and immunity. Thirteen vitamins have been identified for humans; most are obtained from food, and their deficiencies lead to specific diseases.
When to take vitamins
For vitamins and minerals there is no single best time that suits everyone. Timing covers the relationship to meals, the interval from another supplement or medicine taken at the same time, and being able to use it regularly. Time of day is the item with the weakest evidence among these.