This study examined predictors of dietary supplement use in a population-based sample of cancer survivors of the 10 most common cancers. Sixty-nine percent (69%) of participants reported using dietary supplements after their cancer diagnosis. Since participants were an average of 18.8 months postdiagnosis, this provides an estimate of any dietary supplement use among short-term cancer survivors. This figure is at the higher end of estimates of CAM use within the current literature, especially given that it focused only on one form of CAM: dietary supplements. The high rate may in part be due to the inclusion of multivitamins and herbal products as part of dietary supplements. In this population, multivitamins and green tea were the two most commonly reported products. Multivitamins were seen as the most commonly used form of CAM (80.3%) in a small sample of veterans with cancer.19
A study of patients with breast, prostate, and colorectal cancer also found that 48.0% started taking a new dietary supplement after diagnosis20
and in the Women's Healthy Eating and Living Study, 80.9% of women with breast cancer reported use of dietary supplements.22
Finally, a recent survey among European cancer survivors found that herbal medicines and remedies were the most popular form of CAM and that rates of use after diagnosis tripled.32
Additional population-based studies isolating dietary supplements as a form of CAM are needed to determine whether utilization is comparable among other cancer survivors.
Similar to previous studies of overall CAM use and dietary supplement use among patients with cancer, the demographic characteristics of female gender7,12,16,17,21,27,32–35
and higher education19,22,32,34,35
were associated with supplement use. A recent review of vitamin and mineral supplement use (excluding herbal supplements) among U.S. adult cancer survivors concluded that these factors were most consistently associated with use.28
Although some studies have identified younger age7,8,10,18,32,34
as a correlate of CAM use, age was not a significant predictor in this population. Instead, survivors 55 and over tended to use supplements more than those less than 55. Our findings are similar to the increased use of dietary supplements seen among older colon cancer survivors after diagnosis,21
older patients with breast cancer,22
and older adults (with and without cancer).24,27
general health subscale was not associated with use of supplements. Other analyses among patients with colorectal cancer,7
and a range of advanced18
and nonadvanced cancers34
found that utilization of CAM was associated with poorer health status. Although not significant in this population, supplement use tended to be higher among those survivors with better general health ratings. Since the SF-36®
was administered after cancer diagnosis and concurrently with the assessment of supplement use, we were unable to determine the temporal relationship between these characteristics.
Several other studies of patients with cancer have observed associations between CAM use and clinical variables, such as greater number33,36
and intensity of symptoms,36
as well as more progressive cancers,37
and receiving standard treatment for cancer,32,33
but none of the clinical variables in this population were associated with supplement use. The variation in clinical correlates may be due to the fact that this analysis addresses only dietary supplement use whereas others studies have explored all forms of CAM. In addition, the participants in this study were an average of 18.8 months postdiagnosis, with many not currently undergoing active treatment. Thus, both the number and intensity of symptoms may have abated following the cessation of treatment.
One of the strengths of this study is the general population-based sample of cancer survivors with registry confirmed diagnoses. Although most SCS-I Connecticut participants completed the DSI, the participation rate for SCS-I in Connecticut was 42.9%, introducing the possibility of response bias. However, the overall response rates for SCS-I were comparable to other national surveys.29
Since most participants enrolled in SCS-I within 2 years of cancer diagnosis, poor recall of events should be limited. Our analysis was limited in some ways, as the DSI did not comprehensively assess dose, duration, or exact time of initiation of use. Other research has found associations between specific cancer types and the use of certain supplements,16
and this should be explored further in larger samples. In an observational study such as this, it is possible that the findings may be due to confounding by unmeasured variables. However, the SCS-I questionnaire comprehensively gathered information on a wide range of demographic and clinical characteristics. Finally, there is the possibility of survival bias, as individuals who died between diagnosis and recruitment for SCS-I may have had a different pattern of CAM use.
Interestingly, the majority of patients in this population taking dietary supplements after their cancer diagnosis informed their physician of this use. In the U.S. general population, less than 40% of people using CAM told their physician.3
One study of newly diagnosed cancer patients undergoing treatment found that a little more than half of patients told their physician about their CAM use.7
Among cancer patients using vitamins or minerals, a recent review found that 31%–68% did not inform their physicians.28
Since our estimate is slightly higher than previous studies, our population may not be nationally representative. In our population, 47.3% of patients reported getting information on dietary supplements from their doctor. With numerous visits to physicians during cancer treatment, our participants had multiple opportunities to ask their doctors about a range of topics. We did not ask the participants whether their physicians were recommending dietary supplement use, only whether they were a source of information, and we are unable to determine whether the physician or the cancer survivors brought up the topic of dietary supplements. In support of our findings, one study of cancer survivors found that patients were more likely to report CAM use to their doctor if the CAM therapy was related to diet or herbal medicine.6
Participants reported taking a wide range of dietary supplements after cancer diagnosis. Of note, 23% of the cancer survivors reporting using vitamin C, which was recently found to diminish the effectiveness of chemotherapy agents used during cancer treatment.39
Little is known about the effects of dietary supplements on cancer survivors, especially when undergoing treatment. The sharing of information between patient and clinician is important as it would enable physicians to monitor potential contraindications between CAM therapies and traditional treatments.
Many of the patients in our sample obtained information on supplements from friends and family, as well as magazines or books. Similar sources of information on CAM were identified in a European-based sample.32
It is important to note that the quality of information from these sources varies widely and may not provide appropriate information for patients with different cancer diagnoses, especially those undergoing active treatment. Although in our study relatively few patients (7.9%) obtained information from the Internet, we saw that younger cancer survivors were more likely to obtain information on dietary supplements from this source. A recent analysis of Internet information on breast cancer found a low prevalence of inaccurate statements (5.2%), but webpages containing CAM information were 15.6 times more likely to contain inaccurate statements than webpages that did not contain information about CAM.40
Physicians should ask cancer survivors about dietary supplement use, as they can be a valuable avenue for patients to obtain accurate and appropriate information.