**1. Introduction**

Vitamin C is known as the antiscorbutic vitamin. Vitamin C, whose discovery began with scurvy treatment research, is known as ascorbic acid due to its Latin origin, 'scorbutus, hence 'a-scorbutus'. This definition also includes L-dehydroascorbic acid, which is easily converted to ascorbic acid in the human body [1, 2].

The most important advocate of vitamin C in history is Linus Pauling, winner of the Nobel Prize in Chemistry and the Nobel Peace Prize [3]. All of Pauling's ideas about the benefits of vitamin C in fighting colds and cancer were rejected at the time [4].

For many years, different doses and therapeutic forms of vitamin C have been used to treat colds [5]. Researchers believe that this activity is due to its immunomodulatory role on the immune system, which promotes T cell development [6]. There have also been studies that show parenterally administered vitamin C has chemotherapeutic efficacy in cancer treatment [7]. In many biochemical reactions in the body, vitamin C acts as an electron donor or reducing agent. Vitamin C is used in chronic hemodialysis patients to both prevent and repair oxidant damage to DNA, lipids, and proteins by reducing intracellular reactive oxygen species (ROS) [8, 9]. In addition, it acts as a cofactor for 8 basic enzymes. It is also essential for the biosynthesis of collagen, catecholamines, and carnitine in the body [10].

In recent years, studies have revealed that vitamin C, which has been studied in such a wide range of therapeutic areas, has negative effects, particularly at high doses. Vitamin C has antioxidant activity in low doses and pro-oxidant activity in high doses, according to studies. The chemotherapeutic efficacy, especially in the parenteral use of high doses, is also based on this basis. Furthermore, one study observed that oral administration of doses greater than 2 g causes osmotic diarrhea and painful abdominal distension [11]. Similarly, polyuria has been reported following parenterally high-dose vitamin C administration [2].

In the light of past and present research, the therapeutic efficacy of vitamin C is still unclear, as are its adverse effects. Because ascorbic acid participates in drugs and antioxidant diet contents in different combinations and different forms. In addition, the data obtained from the studies also differ. Considering the differences between oral and parenteral use of ascorbic acid, it is usual to have differences of opinion among physicians regarding the daily use of ascorbic acid in treatment [4]. Studies that clarify vitamin C's therapeutic efficacy will provide the foundation for its widespread safe use.

The debate regarding the beneficial effects of vitamin C on living organisms is still ongoing. The only clinical trial of vitamin C that has been proven is its prophylactic and therapeutic effect on scurvy [4].

Following absorption, vitamin C levels rise in the blood and then in the tissues. There is no excretion in the urine during this time. Following this, levels begin to decrease in tissues, first in the blood and then in leukocytes and platelets. In individuals without any renal function problems, most of the surplus metabolized in the blood and tissues is excreted in the urine [12]. Vitamin C is metabolized into oxalate. Oxalate formation potentially leads to kidney stone formation [2].

Efficacy studies on the kidney are also common in vitamin C research. However, there are differences of opinion on the adverse effects of vitamin C on the kidney. The effect of vitamin C on the kidney was evaluated in this study by incorporating various viewpoints.
