[Health Tip!] 'Vitamin C Good for Lung Cancer?' No Effect as a Supplement

A study has found that vitamin C, known to reduce the risk of lung cancer, actually lowers the risk when consumed through food, but has no effect when taken as supplements such as vitamins.

Mandarins known to be rich in vitamin C

Seung-Kwon Myung, Dean of the Graduate School of International Cancer Studies at the National Cancer Center and a specialist in family medicine, revealed that this was confirmed through a meta-analysis of 20 cohort studies published in international journals from 1992 to 2018.

Dr. Myung, an expert in meta-analysis, stated, "We conducted a meta-analysis by synthesizing the results of 20 cohort studies finally selected through literature searches in major medical databases PubMed and EMBASE. The overall relative risk (RR/HR) between vitamin C intake and lung cancer risk was 0.90, indicating no significant association."

However, subgroup meta-analysis by source showed that the effect of reducing lung cancer risk varied depending on the method of intake. In 14 cohort studies where vitamin C was consumed through food, the relative risk of lung cancer was 0.82, showing an 18% reduction (95% confidence interval 0.73-0.92), whereas in 4 cohort studies where vitamin C was taken as supplements, the relative risk was 1.01 (95% confidence interval 0.84-1.22), showing no significant difference.

Dr. Myung, the lead author of the study, explained, "When epidemiological studies observing people worldwide over several decades are combined, it is known that sufficient intake of fruits and vegetables reduces the incidence of cancer and cardiovascular diseases by about 30%. One reason for this is that fruits and vegetables are rich in antioxidants that suppress reactive oxygen species that cause cancer."

He continued, "Vitamin C is one of the powerful antioxidants, and consuming fruits and vegetables rich in vitamin C can prevent many types of cancer, especially lung cancer, which accounts for the highest mortality rate from cancer. However, among epidemiological studies on humans, the highest level of evidence from cohort studies shows that the preventive effect against lung cancer differs depending on whether vitamin C is consumed through food or supplements. This prompted us to conduct a meta-analysis synthesizing cohort studies to investigate whether there is a difference depending on the source of vitamin C," explaining the background of the study.

Myeong Seung-kwon, Dean of the Graduate School at the International Graduate School of Cancer Studies
[Photo by International Graduate School of Cancer Studies]

He further explained, "The meta-analysis of 20 cohort studies showed that vitamin C intake through food reduces lung cancer risk by 18%, but taking it in the form of supplements such as vitamins had no effect." Regarding the cause of this difference, he proposed two hypotheses. Dr. Myung said, "When vitamin C is consumed through food, other antioxidants and nutrients are also ingested together, which may contribute to the observed cancer-preventive effect, but vitamin C supplements alone may not show such an effect. Another hypothesis is that while reactive oxygen species cause cancer and cardiovascular diseases, they also have a positive function in eliminating microbes and external substances. Long-term intake of antioxidants like vitamin C may reduce defense and immune functions against external substances, potentially harming health," explaining the difference in effects depending on the source.

Dr. Myung emphasized, "Quitting smoking is absolutely essential for lung cancer prevention. Antioxidants like vitamin C and various nutrients should be consumed in the form of food, not supplements." He added, "According to clinical trials and meta-analyses conducted to date, health functional foods such as vitamins, omega-3 fatty acids, probiotics, calcium, and glucosamine have little or no evidence of health benefits and may even be harmful. Instead of wasting time and money on health functional foods without established clinical evidence, people should prevent cancer and maintain health through proper lifestyle habits such as balanced food intake, regular exercise, and maintaining a standard weight," highlighting the implications of this study.

This study was published online last month in the oncology SCIE international journal Oncology Letters, with Dung V. Tran, a graduate student from Vietnam at the National Cancer Center Graduate School of International Cancer Studies, as the first author, and Dr. Myung as the corresponding author.