The levels of the trace elements in the integrated samples of fingernail and toenail in healthy human subjects observed in this study were comparable to those shown in previous studies27-30. In this study, the mean values of trace element levels in the fingernails and toenails were similar to those shown in the international survey by Takagi et al.28. In the fingernails of both men and women, except for As and Fe, the mean values for the rest of the elements were the same as those measured in the fingernails by Vance et al.27. Meanwhile, As and Fe levels were in agreement with those obtained by Biswas et al.31. The level of Zn in toenail was also in agreement with that obtained by Campos et al.19. The levels of As and Cr in toenail were comparable with those obtained by Johnson et al.20. The levels of the elements including Cr, Co, Fe, Se, and Zn in toenails were consistent with those obtained in both men and women by Sureda et al.29. From the results of observed trace element levels in this study (Table 1 and Table 2) and the previous studies mentioned above, it can be assumed that the selected trace elements did not depend on the source, fingernails and toenails, nor did they depend on the gender.
Currently, in our literature search, we have not found any claims that have investigated the trace element levels in the nails of colorectal cancer patients. Therefore, it was difficult to compare the results obtained in our study with those in other studies. The Se level in the nails of the untreated colon and rectal cancer patients was twice as high as that measured in the toenails by van den Brandt et al.16, although it was the same as that measured by Garland et al.32. There were significant differences in the levels of the elements, including As, Fe, Hg, Sc, Se, and Zn, found in this study, while for the elements such as Br, Co, and Cr there were no significant differences (Table 3). The levels of Co, Cr, Fe, and Se in the nails of patients were found to be of the same degree order of their values in colorectal tumors . Meanwhile, the levels of elements such as Co, Cr, Fe, Hg, Se, and Zn had the same degree order compared to those in colorectal polyps1. Compared with colon tissue as studied by Middle et al.7, the Se level in the nails of colon cancer patients had the same mean value, whereas the Zn level was approximately twice as high. Juloski et al.33 reported that Zn and Se levels significantly differed between the malignant tissue of colorectal cancer and adjacent healthy bowel tissue. This was consistent with our results in the case of Zn and Se levels in the nails. Nail Se and Fe levels have also been linked to the development of stomach cancer34.
Chemotherapy or radiotherapy of colorectal cancer did not affect the levels of the observed elements in this study. All observed elements did not show significant differences between the untreated and treated subjects. In investigating the chemotherapy effect on trace elements in blood serum, Hasan35 showed that chemotherapy did not augment the rates of trace elements such as Zn, Fe, and Se. However, Ahmadi et al.36 indicated that the serum Zn and Fe levels in women after chemotherapy were significantly decreased (p < 0.001), while the serum level of copper increased but was not significant (p = 0.676). We have not found any claims that have studied the effects of chemotherapy or radiotherapy on trace element levels in the nails.
Toxic elements, such as As and Hg, incorporate into the human body through the air, drinking water, and food37,38, and important food sources are fish and seafood39. In this study, As and Hg levels in the nails were found to be significantly different between the healthy group and the patient group, and there was no significant difference between the treated and untreated patients in both colon and rectal cancers. The levels of As and Hg in the patient's nails were higher than those previously found in the unexposed populations27,30,40,41.
Essential elements such as Fe, Se, and Zn play an important role in metabolism in the human body. A deficiency or excess of these elements can lead to chronic disease, sometimes even leading to cancer. The mean concentrations of these elements were higher in the patient group than in the healthy group. Very few reports on the concentration of trace elements in colon cancer patients are available42,43. Relative to Fe, previous studies suggested that high levels of this element induced colorectal cancer in animals and raised the risk of colorectal cancer in humans through the formation of OH radicals and suppression of cellular immune functions44,45. Lee et al.46 suggested that the intake of dietary heme iron was associated with an increased risk of proximal colon cancer. In this study, the Fe level in the nails in the untreated patient group (both colon and rectal cancers) was approximately 1.4 times higher than that in the healthy group. In the case of the Se level in the nail, many previous studies reported on the Se levels associated with colorectal cancer risk. Ghadirian et al.17 have observed a statistically significant inverse association between toenail Se level and the risk of colon cancer (p = 0.009). Meanwhile, van den Brandt et al.16 and Garland et al.14 reported that the Se level in the toenail was not associated with the risk of colon or rectal cancer. Our study revealed that there were significant differences in the Se levels in the nail for both colon and rectal cancer. The Se levels in the nail among the untreated patient groups were approximately 1.5 times higher than those in the healthy group. Although Zn is an essential element, a deficiency or excess leads to the risk of chronic diseases, including cancer. Diet is the primary source of Zn exposure. Average Zn consumption from food ranges from 5.2 to 16.2 mg/day and Zn levels in animal products vary depending on the soil and water concentrations where the animals were raised25. To our knowledge, no studies have examined the Zn level in the nails of colorectal cancer patients. Therefore, the results of this study could not be compared with those of previous studies. Milde et al.7 have reported that there was a statistically significant change in Zn level in the serum of colorectal cancer patients in comparison to the control group. Arriola et al.6 showed that Zn levels in colorectal tumor tissue were higher than those in the normal tissue. In our study, Zn levels in the nails of patients with colon and rectal cancer were approximately 1.5 times higher than those of the healthy subjects.
In assessing the effect of chemotherapy or radiotherapy on trace elements, we observed that there was no significant difference in Fe, Se, and Zn levels between treated and untreated by chemotherapy or radiotherapy. This was agreed with the studied results by Hasan35.
For other essential elements such as Br, Co, and Cr, no significant differences were found in this study. Since no previous studies have examined the levels of these elements in the nails of colorectal cancer patients, a comparison with previous studies was impossible. In the study of trace element levels in the nails of patients with breast cancer, Huynh et al.21 showed that the Br and Co levels did not differ significantly between the control group and the case group, while Cr level did.
In conclusion, this study showed that an integration of fingernail and toenail samples may be used to analyze trace element levels in human disease evaluation. Significant differences in the levels of trace elements including As, Hg, Fe, Sc, Se, and Zn were found between healthy human and colorectal cancer patients. This study showed that there was no significant difference in certain trace element levels between the treated and the untreated patients. The essential elements (including Fe, Se, and Zn) and toxic elements (including As and Hg) were not effacted by chemotherapy or radiotherapy. However, due to limited sample size, the results in this paper might be insufficient to provide a reliable statement on the use of the level of trace elements in nails as an indicator of colorectal cancer. Further investigation using a larger scale of sampling are required for the reliable conclusion on the association of trace elements in the nails with colorectal cancer.
The strength of this study is that this is the first report on the evaluation of trace elements in the integration of fingernails and toenails samples in colorectal cancer patients. Furthermore, an investigation of the effect of chemotherapy or radiotherapy on trace elements in the nails of patients with colorectal cancer was also carried out in this study. However, there are also difficulties in comparing our results with those obtained from previous studies. A limitation of this study was the small sample size in which trace elements are analyzed.