Vitamin C, also known as ascorbic acid, is a water-soluble micronutrient that the body cannot produce on its own, making it an indispensable part of the diet. Many people increase their intake at the first sign of illness, hoping for relief from cold symptoms, including a sore throat. This article examines the scientific evidence regarding vitamin C’s role in supporting the body’s defenses and its specific effectiveness against an existing sore throat.
How Vitamin C Supports Immune Function
Vitamin C is highly concentrated in various immune cells, where it plays a supportive role in the body’s defense mechanisms. It is a powerful antioxidant, helping protect immune cells from damage caused by oxidative stress, which increases during infection or inflammatory response. This protective action helps maintain the integrity and function of the immune system while it fights a pathogen.
The vitamin is necessary for the proper functioning of phagocytes, which are white blood cells that engulf and destroy foreign invaders like bacteria and viruses. Vitamin C enhances their ability to move toward the site of infection and perform microbial killing. It also supports the proliferation and differentiation of T-cells and B-cells, which are central to the adaptive immune response that provides long-term protection. Adequate daily intake is important for maintaining a healthy immune system against the viruses that often cause sore throats.
Research Findings on Sore Throat Relief
Clinical research suggests that taking vitamin C regularly does not prevent the general population from catching a cold, the most frequent cause of a sore throat. However, consistent daily supplementation offers a modest but consistent benefit in reducing the duration and severity of cold symptoms once they begin. In adults, regular intake reduces the length of a cold by about 8%, and in children, the reduction can be up to 14% to 18% with higher doses.
The effect on duration and severity is more pronounced in specific, highly stressed populations, such as marathon runners or soldiers on subarctic exercises. In these groups, prophylactic vitamin C supplementation has halved the risk of catching a cold. For the general public, the evidence is less convincing when the vitamin is taken only after cold symptoms have already started. Trials examining high-dose vitamin C as a therapeutic treatment after symptom onset have shown no consistent effect on either the duration or severity of symptoms.
This suggests that vitamin C’s benefit is primarily prophylactic, supporting the immune system before it encounters a large viral load. Regular intake can decrease the overall severity of the common cold by about 15%. This reduction in severity may translate into a less painful or shorter-lived sore throat, even if the vitamin does not directly target throat inflammation or pain. Therefore, while regular, long-term use may lessen the impact of the cold, a sudden high dose will likely not provide immediate symptomatic relief.
Recommended Intake and Safety
The Recommended Dietary Allowance (RDA) for vitamin C aims to prevent deficiency and maintain adequate plasma levels. For adults, the RDA is 90 milligrams (mg) per day for men and 75 mg per day for women, with slightly higher recommendations for pregnant or breastfeeding individuals. Prophylactic prevention of respiratory infections may require slightly higher daily intakes, generally in the range of 100 to 200 mg per day, to achieve optimal tissue levels.
The Tolerable Upper Intake Level (UL) for vitamin C in adults is set at 2,000 mg per day. This limit is based on the highest daily intake unlikely to cause adverse health effects in most people. Doses exceeding the UL may lead to mild gastrointestinal disturbances, such as diarrhea, nausea, and abdominal cramping, due to the osmotic effect of unabsorbed vitamin C in the gut.
People with a history of kidney stones should exercise caution with high-dose supplementation. Excessive intake can increase the excretion of oxalate in the urine, potentially contributing to stone formation in susceptible individuals. Therefore, while some research suggests benefits from higher doses during illness, it is important to remain below the 2,000 mg daily upper limit to ensure safety and avoid unpleasant side effects.