Barion Pixel
Riavita logo
Close this search box.
Riavita Vitamin C+D with Quercetin

Science behind

Vitamin C and D +Quercetin

The role of vitamins in health maintenance is an important area of research to this day

Research on the effects of vitamins mostly focuses on eliminating deficiency and restoring normal physiological functions. If the condition of the disease improves after vitamin supplementation, it can be assumed that the given vitamin has a role in the process. Recently more and more research is emerging that specifically addresses the health effects of extra daily intake of vitamins.

As an antioxidant, Vitamin C supports the immune system in a relatively non-specific way through the balance of oxidative processes. Although the recommended minimum daily intake is 80 mg, many researchers are interested in the effect of a daily vitamin C intake of 1000 mg on various diseases.

According to studies focusing on the common cold with a runny nose, although vitamin C has a slightly preventive effect, it can reduce the length and severity of the illness.

Therefore, adequate vitamin C intake is required. Vitamin C does not play an exclusive function in immunity; it can be more effective when paired with other vitamins and antioxidants, especially flavonoids. Vitamin C, in addition to being a potent antioxidant, can have a role in the infection-induced T-cell response and the modulation of immune system-activating cytokines.

Vitamin D supports the immune system in a much more specific way. The active form of vitamin D (1,25-dihydroxyvitamin D3) has a hormone-like effect and acts on cells through nuclear receptors.

The immunomodulatory function of Vitamin D minimizes the chance of developing autoimmune diseases and counteracts immunological “overactivity.”


Serum levels of both vitamin C and vitamin D are known to be inversely related to tiredness, meaning that their deficiency leads to fatigue and tiredness.

In a study of 62 people, participants who complained of general body, neck, and back pain and fatigue were treated with vitamin D, and as a result, their condition began to improve rapidly.

During the recovery phase, stroke survivors have a high degree of tiredness and depression. According to a British study, vitamin D deficiency is one of the causes as all participants who received vitamin D supplementation had improved measures. The results were also confirmed in a Chinese study of more than 500 patients recovering from an ischemic stroke.


It has been known since the 1940s that vitamin C deficiency can lead to high cholesterol and triglyceride levels. In severe vitamin C deficiency, cholesterol can build up in the liver to the point that it can harm the liver cells.

In people with vitamin C deficiency, supplementing the right amount of this vitamin has reduced blood cholesterol levels and improved cardiovascular performance.

Scurvy is a classic vitamin C deficient condition, in which capillary walls become weak and brittle, and bleeding ensues. Vitamin C is a co-factor in collagen synthesis, thus if it is not present in appropriate amounts, the structure of the vessel wall will be compromised and it becomes leaky.


The Basics

Science behind

Examined effects, special areas...

Product page

Vitamins are essential for the normal functioning of our body. Inadequate vitamin intake can lead to deficiency diseases that are worsening within weeks or even days.

To avoid this, experts have defined the minimum daily intake. In the case of water-soluble vitamins it is worth ingesting the determined minimum, while in the case of fat-soluble vitamins, it is also good if the ingestion is uneven through the days of a week unless, every week, a sufficient amount is consumed. In addition, the daily upper level of vitamin intake (the amount that can be safely ingested) is very high, thus it is difficult to overdose them. For example, Vitamin C and Vitamin D can be consumed in several times higher amounts than the minimum recommendation, without putting a burden on the body. Moreover, many scientific research papers suggest that it is not only recommended to ingest the right amount of daily dose but is preferred to exceed it in certain cases, as extra vitamin intake can be beneficial for health.

Vitamin D

Vitamin D is unique among vitamins both in the terms of structure and properties. Fat-soluble, so our body can store it for up to a month. Still, even a large daily intake is considered safe. Currently, the tolerable daily upper limit is 4000 IU (international unit). Vitamin D is commonly known as a main supporter of the immune system: it makes us more resistant to certain infections. Additionally, it helps the absorption of calcium and phosphorus and in the proper growth and development of bones and teeth. Moreover, its antidepressant-like effect was also observed. Insufficient Vitamin D levels lead to fatigue, muscle weakness, physical pain, and more fragile bones.

Vitamin C

Perhaps the best-known and most popular vitamin. Vitamin C was discovered by Albert Szent-Györgyi in 1928 when he was looking for a cure for scurvy. Later, he was awarded the Nobel Prize in 1937 for his exploration of the cellular oxidation processes, including the antioxidant role of vitamin C. Vitamin C became the antidote to scurvy, which he could extract from lemon juice and Hungarian red pepper in an amount that was sufficient to treat his patients.

Ever since Vitamin C is one of the most commonly used substances in disease-preventing home remedies, it is available in many forms and combinations. By supporting our antioxidant system, it protects the body against free radicals coming from our environment or produced in our body. Among the many functions of vitamin C, the most important is reducing the risk of certain chronic cardiovascular diseases, reducing the chance of developing gout by lowering uric acid levels and helping to absorb iron, and supporting the normal functioning of the immune system. Many people say that it also plays an important role in preventing and treating colds.

Vitamin C works with many other antioxidants to help regenerate each other while keeping free radicals under control. With dietary antioxidants, e.g. together with a flavonoid called quercetin, the antioxidant capacity can be significantly increased.


Quercetin is a natural flavonoid, which has been detected in almost all plants to a greater or lesser extent. It plausibly has a role in the prevention of chronic diseases (such as cardiovascular diseases), and there are also scientific papers reporting its immune system-supporting effect and its direct antiviral effect.