Through this present study, we identified the effect of chemotherapy time, nutritional status and also the interaction between the chemotherapy time and the nutritional status of women with BC on the domains and symptoms of HRQoL. Overweight women; WC indicative of increased risk and substantially increased risk of metabolic complications; WHR indicative of risk of developing chronic diseases; WHtR indicative of excess abdominal fat; that is, women with a worse nutritional status or on a more advanced time of treatment (T1 and T2) presented worse scores on important domains of HRQoL. It is important to highlight that the nutritional status, in isolation, had a statistically significant effect, demonstrating the importance of seeking a healthy nutritional status to minimize the negative impact on HRQoL during the treatment. We also observed that overweight, higher WC and WHtR and the interaction with CT time negatively impacted the global function, that is, they presented a worse quality of life and physical condition at the end of the treatment (T2 ≠ T0). .
Women with BC, when compared with the population free of the disease, show a decrease in HRQoL [12]. Added to that, antineoplastic treatments are also associated with a HRQoL decrease [25]. .
Besides that, we identified a decrease in the scores of physical function, which was associated with higher levels of BMI, WC, WHR, WHtR and longer CT times. Factors related to the disease and treatment such as cardiotoxicity, neurotoxicity, lymphedema, precocious menopause, sexual disfunction, infertility, secondary leukemia, weight gain, difficulty sleeping and fatigue can justify the negative impact on HRQoL and physical function [26]. Added to that, there is the fact that a worse nutritional status, characterized by BMI, WC, WHR, WHtR measures, can be associated with a worsening physical function, as identified by Mosher et al, 2009, where an association with BMI was found. Mosher et al (2009) also identified that better diet quality and exercise are associated with better physical function (better vitality and physical function p ≤ 0.05)[27] .
We also observed a significant impact of the interaction of CT time and higher levels of BMI, WC and WHR on the insomnia score.. Among the factors that can be related to this problem, it is the presence of menopause symptoms caused by CT or hormonal therapy such as hot flashes [28] and also biological modifications related to the cancer and treatment, which includes changes in pro-inflammatory cytokines and the hypothalamic-pituitary-adrenal axis (HPA) [29].
Sexual function was also significantly impacted by the interaction between CT time and higher WC and WHR.. A study by Biglia et al. (2010)[30] evaluated the impact of BC treatment on sexual function, cognitive function and body weight on pre-menopause women, and identified that at T0 (baseline, first week after the surgery) 77.1% of the sample (n = 35) reported sexual activity during the 4 previous weeks, which reduced to 37.1% at T1 (after the adjuvant CT or after at least 6 months of hormonal therapy) and to 34.3% at T2 (one year after surgery). It also became evident in Biglia et al (2010) study, that they had a weight gain (T0 = 65.19; T1 = 67.26; T2 = 67.21) with a difference of + 2.07 between T0 and T1 (p = 0.035) and + 2.02 between T0 –T2 (p = 0.049) [30].
Higher BMI and CT time, as well as the interaction of WHtR with CT time, impacted negatively on the fatigue score. Among the factors that can be related to this problem it is that, BMI and CT are associated with the increase of receptor two of tumoral necrosis factor (TNF-RII), which has been related to higher fatigue scores [31]. The TNF-RII is a receptor of the alfa tumoral necrosis factor (TNF-α), an inflammatory mediator [32]. A study performed on mice found that the adipose tissue is related with the production of TNF-α [33] and obese humans have a higher production of this cytokine than normal weight individuals [34].
We also identified a decrease in the physical function score, associated with higher BMI and WC, longer CT time and the interaction between BMI, WC, WHR and WHtR with CT time. Nutritional status influences the HRQoL not just on BC, but also on colorectal cancer; an elevated WC is also associated with a worse physical function and higher scores of fatigue in men and women [35]. CT time also influences the HRQoL of these women, worsening the social function domain.. Among the factors that could be related to this issue, is the possible occurrence of nausea and vomiting due to CT [36]..
Pain was also affected by CT time, where the score worsened throughout the treatment. The mechanisms involved in the pain process are not very clear, but it is known that CT acts on nociceptors and glia modulators, activating the microglia and astrocytes of the spinal medulla, and these release neuromodulators related to pain, causing chronic pain [37].
In the face of the shown facts, it becomes clear the need to reinforce the improvement of changeable factors that can increase the survival of these women, through a healthy diet, regular physical activity, and consequently an adequate nutritional status, with the purpose of achieving a better HRQoL, because CT itself already causes an 0.55 odds ratio of mortality in 10 years [38].
A systematic review that included 63 studies randomized 5761 women in two groups, one intervention (physical activity, n = 3239) and the other control (n = 2524), revealed that the physical activity intervention resulted in small to moderated improvements in HRQoL, emotional function, self reported and measured physical function, anxiety, cardiorespiratory capability and fatigue. However, these results must be interpreted carefully because the quality of evidence is small to moderated, due to heterogeneity of the interventions and measure of results [26].
The study of Phillips et al (2015)[39], also demonstrated that maintaining or increasing physical activity during the post diagnosis time was significantly and independently associated with lower fatigue, depression and stress scores and higher values for physical well-being, physical, social, emotional and functional scores, specific to BC and global HRQoL (effect size = 0.23 a 0.60). Maintaining or losing weight had an independent association (p < 0.05) with lower fatigue, higher physical well-being specific for BC and general HRQoL (effect size = 0.28 a 0.87).[39].
With regard to food intake, the dietary pattern is a factor of influence on HRQoL of BC survivors, and the ones with a healthier diet, have a better HRQoL, presenting better role function, emotional function, cognitive function, social function and global health status [10]. Assaf et al (2016) verified that a change in diet, with a reduction of 20% of daily calories in fat, eating fruits and vegetables 5 times per day and grains 6 times per day, caused an improvement in HRQoL[40] and a better HRQoL is associated with a better overall survival after 1 year of diagnosis [41] .
It becomes evident that modifications in changeable lifestyle factors directly affect the nutritional status, and consequently, can achieve significant improvements in HRQoL. Furthermore, it has the potential to contribute to a better prognosis [42] and a lower mortality rate in 10 years [38].
About the possible limitations of this study, it is important to consider that BMI is a method to classify the nutritional status of individuals, but is acknowledged that it is a limited method, and there may be overestimation or underestimation of the real nutritional condition. Even though, we highlight that all the measurements, including interviews, were performed by trained nutritionist.
Considering the fact that there are only a few articles in the literature that have investigated the relationship between nutritional status and HRQoL, we highlight the contribution of these results, especially because this is the first prospective study analyzing the effects the association between nutritional status and CT time has on HRQoL of BC women.