This systematic review and meta-analysis investigated the association between Vitamin C intake and the risk of digestive system cancers (DSC). The study analyzed 32 prospective studies involving over 1.6 million participants. The findings revealed a significant negative correlation between Vitamin C intake and DSC risk, with higher intake linked to a reduced risk of cancers, particularly oral, pharyngeal, esophageal, stomach, and colorectal cancers. The study emphasizing the importance of a balanced diet and appropriate supplementation.
When we talk about vitamins, it's hard not to be familiar with them—vitamins A, B, C, D, E, and more are essential nutrients for our bodies. They vary in types, functions, and benefits. Among these, Vitamin C is one of the most common vitamins, with abundant food sources, especially in fresh vegetables and fruits like cabbage, spinach, strawberries, and citrus.
As an important antioxidant, Vitamin C has been shown to play a key role in preventing various chronic diseases. It not only boosts the immune system and promotes collagen synthesis but also has potential effects in eliminating free radicals and inhibiting tumor growth. However, excessive intake of Vitamin C can put a burden on the body, potentially causing diarrhea, gastric bleeding, and other issues. Many chronic diseases can accumulate over time, eventually developing into cancer. So, is there a link between Vitamin C intake and the risk of digestive system cancers (DSC)?
Recently, researchers explored this question in a study published in Food & Function, titled “Association between dietary vitamin C intake/blood level and risk of digestive system cancer: a systematic review and meta-analysis of prospective studies.”
This systematic review and meta-analysis involved a comprehensive search of scientific literature in three major databases (PubMed, EMBASE, and Web of Science) using search terms related to Vitamin C, antioxidants, and various digestive system cancers, up until September 9, 2023. Following pre-set inclusion and exclusion criteria, 32 prospective studies involving 1,664,498 participants were included.
Overall Association between Vitamin C Intake and Digestive System Cancer Risk
The study found a significant negative correlation between Vitamin C intake and the risk of DSC. Specifically, the highest levels of Vitamin C intake were associated with a reduced risk of DSC compared to the lowest levels (Relative Risk (RR) = 0.88, 95% Confidence Interval (CI) 0.83-0.93). This suggests that increasing Vitamin C intake may help reduce the risk of digestive system cancers.
Figure 1. Forest plot of the association between dietary vitamin C intake and digestive system cancer
The researchers also conducted subgroup analyses to explore the relationship between Vitamin C intake and specific types of cancer:
- Oral, Pharyngeal, and Esophageal (OPE) Cancers: Vitamin C intake was significantly negatively associated with the risk of OPE cancers (RR = 0.81, 95% CI 0.72-0.93), particularly oral cancer (RR = 0.46, 95% CI 0.30-0.71). In other words, higher Vitamin C intake was linked to lower risks of these cancers, likely because Vitamin C helps eliminate free radicals and reduces cell damage.
- Stomach Cancer: Vitamin C intake was significantly negatively associated with stomach cancer risk (RR = 0.81, 95% CI 0.68-0.95), suggesting that increasing Vitamin C intake may help reduce stomach cancer risk. This could be due to Vitamin C's ability to inhibit the growth of Helicobacter pylori, a major cause of stomach cancer.
- Colorectal Cancer: Vitamin C intake was negatively associated with colorectal cancer risk (RR = 0.89, 95% CI 0.82-0.98), with a stronger protective effect for colon cancer (RR = 0.87, 95% CI 0.77-0.97) compared to rectal cancer (RR = 1.00, 95% CI 0.84-1.19). This may be because Vitamin C helps promote intestinal motility and facilitates the elimination of carcinogens.
- Pancreatic Cancer: No significant association was found between Vitamin C intake and pancreatic cancer risk (RR = 0.97, 95% CI 0.86-1.09), which may be due to the more complex mechanisms of pancreatic cancer, where Vitamin C alone may not be sufficient for prevention.
Figure 2. Subgroup analysis of the relationship between vitamin C intake/plasma vitamin C and digestive system cancer risk
Association between Blood Vitamin C Levels and Digestive System Cancer Risk
The study also found a negative correlation between blood Vitamin C levels and the risk of digestive system cancers, particularly stomach cancer. This may be because Vitamin C acts as an antioxidant in the blood, protecting the gastric mucosa. Specifically, individuals with the highest blood Vitamin C levels had a significantly lower risk of stomach cancer compared to those with the lowest levels (RR = 0.74, 95% CI 0.59-0.92).
Figure 3. Forest plot analysis of the association between blood vitamin C levels and digestive system cancer
Relationship between Vitamin C Intake and Specific Types of Cancer Risk
To further understand the relationship between Vitamin C intake and cancer risk, the researchers conducted a dose-response analysis. They found the following optimal daily Vitamin C intakes for maximum protection:
- For OPE cancers, 250 mg of Vitamin C per day provided the strongest protective effect.
- For stomach cancer, 65 mg of Vitamin C per day provided the strongest protective effect.
These findings suggest that moderate Vitamin C intake may be important for preventing specific types of digestive system cancers. Of course, this doesn't mean that Vitamin C is a cure-all. Excessive intake may lead to side effects such as diarrhea and kidney stones. Therefore, it's important to follow appropriate intake guidelines, preferably through a balanced diet. For example:
- One cup (about 120 ml) of fresh orange juice provides about 120 mg of Vitamin C.
- One serving (about 150 g) of bell peppers provides about 150 mg of Vitamin C.
- One medium-sized kiwi provides about 64 mg of Vitamin C.
- Six strawberries (about 150 g) contain approximately 80 mg of Vitamin C.
- Half a medium-sized red bell pepper provides about 75 mg of Vitamin C.
Figure 4. Dose-response relationship between dietary vitamin C intake and OPE cancer risk
Additionally, the study found that responses to Vitamin C may vary across different populations, potentially due to genetic background, dietary habits, and other factors.
In conclusion, this systematic review and meta-analysis provide strong evidence for the relationship between Vitamin C intake and digestive system cancer risk. It suggests that adequate Vitamin C intake may significantly reduce the risk of certain types of digestive system cancers, particularly oral, pharyngeal, esophageal (OPE) cancers, stomach cancer, and colorectal cancer.
Conclusion
To meet the recommended daily intake of Vitamin C, we can consume more fresh fruits and vegetables. For example, a cup of orange juice with a few strawberries, or some bell peppers and a kiwi, can easily provide the daily required amount of Vitamin C! In addition to getting Vitamin C from food, we can also supplement with Vitamin C supplements to obtain extra nutrition. More effective than regular Vitamin C is liposomal Vitamin C. Since liposomes form structures similar to cell membranes, they can interact with the intestinal cell membranes, promoting more efficient absorption. The liposomal encapsulation can deliver Vitamin C or other nutrients directly into the cells, avoiding the degradation and metabolic loss that regular supplements experience in the digestive tract. Traditional Vitamin C supplements often require large amounts to achieve effective bioavailability, while liposomal Vitamin C allows the body to absorb more active ingredients with a smaller dose. This not only improves supplementation efficiency but also reduces unnecessary digestive burden, helping us better supplement the nutrients we need.