Prof. Dr. Halis Köylü, Head of the Department of Physiology at Üsküdar University Faculty of Medicine, made important statements regarding when, how, and in what form vitamins should be taken.
Improper use of vitamins leads to metabolic deficiencies
Prof. Dr. Köylü emphasized that vitamins are simple compounds necessary for normal body functions, and because they cannot be produced by the body, they must be obtained through food. He said, “They are naturally found in foods. Today, some vitamins are produced synthetically. Vitamins are organic compounds required in small amounts for normal body metabolism but cannot be synthesized in body cells. Vitamin requirements vary depending on body size, growth rate, exercise level, illness and fever, pregnancy, and lactation (lactating women have a special need for vitamin D). The absence of vitamins in the diet or their improper pathological utilization leads to metabolic deficiencies.”
Vitamins can degrade upon contact with oxygen, sunlight, heat, and metals
Prof. Dr. Halis Köylü also explained that vitamins are resistance-boosting and regulatory organic molecules that are not digested, do not become part of cell structure, and do not provide energy. He stated, “Some vitamins function as coenzymes (organic molecules that increase the activity of enzymes and help them work) in the structure of enzymes. A deficiency of these vitamins halts biochemical reactions. Vitamins can degrade upon contact with oxygen, sunlight, heat, and metals (such as copper and iron).”
13 vitamins identified to date
Prof. Dr. Halis Köylü noted that 13 vitamins have been identified to date: A, B complex (B1, B2, B3, B5, B6, B7, B9, B12), C, D, E, and K, and continued as follows:
“Nine vitamins (B complex and C vitamins) are classified as water-soluble vitamins, while four vitamins (A, D, E, and K vitamins) are classified as fat-soluble vitamins. Water-soluble vitamins are generally easily obtained from food, readily absorbed, and easily excreted from the body. Therefore, water-soluble vitamins are stored very little in the body. However, vitamin B12 is an exception. Vitamin B12 is stored in the liver in amounts sufficient for 3-4 years. Water-soluble vitamins are consumed very quickly because they are stored very little in the body. Fortunately, many foods are rich in these vitamins. On the other hand, fat-soluble vitamins are poorly absorbed in the absence/deficiency of bile and/or pancreatic enzymes; their absorption requires them to be taken with fats in food. Fat-soluble vitamins are very well stored in the body and cannot be easily removed. Therefore, high doses of fat-soluble vitamins are toxic to the body.”
Vitamins act as catalysts in converting nutrients into energy
Prof. Dr. Halis Köylü also stated that vitamins are necessary for performing specific cell functions, and explained:
“Most water-soluble vitamins function as coenzymes for various enzymes. Unlike water-soluble vitamins, fat-soluble vitamins generally do not have a coenzyme role; only one (vitamin K) has coenzyme function. Vitamins do not provide energy but act as catalysts in converting nutrients into energy. They accelerate chemical reactions without changing themselves. For this, vitamins are needed in very small amounts. Each vitamin has a different role in the body; some act as antioxidants, while others are effective in tissue growth and differentiation. Some act similarly to hormones. Vitamin A is involved in vision, most B complex vitamins in regulating metabolic events (as coenzymes), B9 (folic acid) and B12 vitamin (cobalamin) in blood formation, vitamin C in strengthening the immune system and wound healing, vitamin D in calcium absorption from the intestines and its deposition in bone, vitamin E in reproduction, and vitamin K in clotting.”
Babies need more vitamin K intake through food
Prof. Dr. Halis Köylü stated that vitamin D is synthesized in the skin under the effect of sunlight, vitamin K and biotin (vitamin B7) are produced by intestinal bacteria, and vitamin B12 is especially stored in high amounts. He said, “Therefore, deficiencies of these vitamins solely due to dietary intake are rare. Because babies have less intestinal flora and fewer vitamin K stores, they require more vitamin K intake through food compared to adults.”
Improper vitamin intake leads to metabolic deficiencies
Prof. Dr. Halis Köylü also explained that vitamin requirements vary depending on body size, growth rate, exercise level, illness and fever, pregnancy, and lactation (lactating women have a special need for vitamin D). He said, “The absence of vitamins in the diet or their improper intake leads to metabolic deficiencies. Deficiencies of fat-soluble vitamins are particularly seen in cases where fat absorption in the intestines is impaired. Other intestinal diseases generally affect vitamin absorption, leading to deficiencies of both water-soluble and fat-soluble vitamins.”
How are vitamins absorbed?
Prof. Dr. Halis Köylü also noted that vitamins are defined as small molecules that have a vital role in biochemical reactions in the body and must be taken through food as they cannot be synthesized in the body. He said, “Fat-soluble vitamins such as A, D, E, and K are taken in ester form and require digestion by cholesterol esterase after absorption. Furthermore, these vitamins are largely insoluble in the intestine, and their absorption is therefore entirely dependent on their incorporation into micelles (clusters formed by surface molecules dispersed in a solution). In cases where bile cannot be excreted from the intestine due to the absence of pancreatic enzymes or bile duct obstruction, fat absorption decreases, and consequently, the absorption of fat-soluble vitamins also decreases.”
Most vitamins are absorbed in the upper parts of the small intestine
Prof. Dr. Halis Köylü stated that while most vitamins are absorbed in the upper parts of the small intestine, vitamin B12 is absorbed in the lower part of the small intestine. He added, “Vitamin B12 is absorbed by binding to a protein called intrinsic factor (IF), which is secreted from the stomach. The absorption of vitamin B12 and folic acid, among water-soluble vitamins, is independent of the sodium ion (Na⁺). However, the absorption of the other seven water-soluble vitamins (thiamine, riboflavin, niacin, pyridoxine, pantothenic acid, biotin, and ascorbic acid) occurs together with the sodium ion (Na⁺).”
Excess vitamins also cause diseases
Prof. Dr. Halis Köylü also emphasized that it should not be forgotten that very high doses of fat-soluble vitamins (vitamins A, D, E, and K) are definitely toxic. He said, “Taking vitamins beyond the recommended daily dose can lead to toxic accumulation and associated hypervitaminosis. Excess vitamin A (hypervitaminosis A) can manifest with symptoms such as anorexia, headache, hepatosplenomegaly (enlargement of the liver and spleen), irritability, dermatitis, hair loss, bone pain, and hyperostosis (abnormal bone tissue growth). Excess vitamin D (hypervitaminosis D) is associated with weight loss, widespread calcification in soft tissues, and consequent kidney failure. Excess vitamin E can cause dysfunction of various hormones, disruptions in vitamin K metabolism, impairments in the blood clotting process (coagulation), and impaired leukocyte (white blood cell) functions. Excess vitamin K is characterized by digestive system disorders and anemia.”
High-dose vitamin B6 intake also leads to peripheral neuropathy
On the other hand, Prof. Dr. Halis Köylü noted that due to their rapid elimination from the body, high doses of water-soluble vitamins (folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid) are thought not to cause any problems. He added, “However, it has been shown that high doses of pyridoxine (vitamin B6) intake can lead to peripheral neuropathy (a disease of the peripheral nerves).”
There is no strong evidence that vitamin supplementation prevents cancer development
Prof. Dr. Halis Köylü also stated that many experts recommend multivitamins in amounts not exceeding the daily requirement because their potential benefits outweigh their harms, and concluded his words as follows:
“Provided they are taken in recommended amounts, vitamin supplements are very beneficial for individuals with conditions such as malnutrition, malabsorption, and advanced age. Vitamin supplements ensure adequate intake for vitamins that are highly likely to be deficient (folic acid, vitamin B6, vitamin B12, and vitamin D). However, the evidence is insufficient to recommend or reject vitamins A, C, or E, folic acid-containing multivitamins, or antioxidant combinations for protection against cancer or cardiovascular diseases. Most experts are against the use of single or combined beta-carotene for protection against cancer or cardiovascular diseases. There is no strong evidence that vitamin supplementation prevents cancer development. The general view is that consuming vitamins in the form of fresh fruits and vegetables is more appropriate.”
