This study assessed the patterns of dietary supplement usage among cancer survivors in the United States in a population-based setting. National Health and Nutrition Examination Survey (NHANES) datasets (1999-2016) were accessed, and adult respondents (≥ 20 years old) with a known status of cancer diagnosis and a known status of dietary supplements intake were included. Multivariable logistic regression analysis was then used to assess factors associated with dietary supplements intake. Moreover, and to evaluate the impact of dietary supplements on overall survival among respondents with cancer, multivariable Cox regression analysis was conducted.
A total of 49,387 respondents were included in the current analysis, including a total of 4,575 respondents with cancer. Among respondents with cancer, 3,024 (66.1%) respondents reported the use of dietary supplements; while 1,551 (33.9%) did not report the use of dietary supplements. Using multivariable logistic regression analysis, factors associated with the use of dietary supplements included:
- older age (OR: 1.028; 95% CI: 1.027-1.030);
- white race (OR for black race vs. white race: 0.67; 95% CI: 0.63-0.72);
- female gender (OR for males vs. females: 0.56; 95% CI: 0.53-0.59),
- higher income (OR: 1.13; 95% CI: 1.11-1.14),
- higher educational level (0.59; 95% CI: 0.56-0.63),
- better self-reported health (OR: 1.36; 95% CI: 1.17-1.58),
- health insurance (OR: 1.35; 95% CI: 1.27-1.44),
- history of cancer (OR: 1.20; 95% CI: 1.10-1.31).
Using multivariable Cox regression analysis and within the subgroup of respondents with a history of cancer, the use of dietary supplements was not found to be associated with a difference in overall survival (HR: 1.13; 95% CI: 0.98-1.30).
The authors concluded that dietary supplement use has increased in the past two decades among individuals with cancer in the United States, and this increase seems to be driven mainly by an increase in the use of vitamins. The use of dietary supplements was not associated with any improvement in overall survival for respondents with cancer in the current study cohort.
Many cancer patients, when they first get diagnosed, are tested for vitamin D levels and found to be low or borderline. Consequently, they get a prescription for supplements. Other than this, there is rarely an indication to take any vitamins or other dietary supplements. Yet, cancer patients take them because they think these ‘natural’ preparations can do no harm (and because the industry can be persuasive [there is big money at stake] and the odd breed of ‘integrated’ oncologists might even recommend them). Sadly, this assumption is not correct. The biggest danger, in my view, is the possibility of supplements to interact with one of the many drugs that cancer patients need to take. So, in a way, it is reassuring that, on average, there is no detrimental effect on overall survival.
The paper will probably also reignite the perennial discussion about the effects of vitamin C on the natural history of cancer. My understanding is that there is none (and this verdict seems to be supported by the findings reported here). But I am, of course, aware that this is a ‘hot potato’ and that some readers will think differently. To them I say: please show me the evidence.