Radiotherapy is one of the major treatment options for malignant neoplasms. Nearly half of all newly diagnosed cancer patients will receive radiotherapy at some point during treatment and up to 25% may receive radiotherapy a second time [1]. While radiotherapy destroys malignant cells, it adversely affects the surrounding normal cells [2]. Acute radiation-associated side effects include fatigue, nausea, diarrhea, dry mouth, loss of appetite, hair loss, sore skin, and depression. Radiation increases the long-term risk of cancer, central nervous system disorders, cardiovascular disease, and cataracts. The likelihood of radiation-induced complications is related to the volume of the irradiated organ, the radiation dose delivered, the fractionation of the delivered dose, the delivery of radiation modifiers, and individual radiosensitivity [3]. Most radiation-induced symptoms are believed to be associated with increased oxidative stress and inflammation, due to the generation of reactive oxygen species (ROS) during radiotherapy, and may significantly affect the patient’s quality of life (QOL) [2].

Hydrogen, a therapeutic medical gas, has antioxidant properties and reduces inflammatory events in tissues [4, 5, 6]. Drinking liquids supplemented with hydrogen represents a novel method of hydrogen gas delivery that is easily translatable into clinical practice, with beneficial effects for several medical conditions, including atherosclerosis, type 2 diabetes, metabolic syndrome, and cognitive impairment during aging and in Parkinson’s disease [7, 8, 9, 10, 11]. Currently, there is no definitive therapy to improve the QOL of patients receiving radiotherapy. Drinking solubilized hydrogen on a daily basis may be beneficial and would be quite easy to administer without complicating or changing a patient’s lifestyle. We hypothesized that oral intake of hydrogen-rich water, generated via a magnesium stick, would reduce adverse events in patients receiving radiotherapy.

To our knowledge, this is the first report demonstrating the benefits of drinking hydrogen water in patients receiving radiation therapy for malignant tumors. This finding may provide the foundation for a clinically applicable, effective, and safe strategy for the delivery of hydrogen gas to mitigate radiation-induced cellular injury. Patients experience GI symptoms and decreased QOL during radiotherapy. These symptoms usually occur as a result of the body repairing damage to healthy cells, are particularly common towards the end of a course of radiation treatment, and can last for some time. The symptoms and their impact on QOL can be worsened by having to travel to the hospital each day. Drinking hydrogen-rich water improved the QOL of the patients receiving radiotherapy and did not require additional hospital visits. Although overall survival of patients with malignant tumors should remain oncologists’ primary concern, survival should also be interpreted in light of symptom palliation and overall QOL, because the side effects of radiotherapy may negate the putative benefit of improved survival. Oral intake of daily hydrogen-supplemented water might be a prophylactic strategy to improve QOL of the patients receiving radiotherapy.

Although the mechanisms underlying the beneficial effects of hydrogen-rich water during radiotherapy have not been clearly elucidated, drinking hydrogen-supplemented water reduced dROM levels and maintained BAP levels in the serum, suggesting hydrogen-rich water exhibits potent systemic antioxidant activity. Previous experimental studies have linked daily consumption of hydrogen-rich water with improvement of a number of conditions in rodent models, including reducing atherosclerosis in apolipoprotein E knockout mice [10], alleviating cisplatin-induced nephrotoxicity [15], reducing vitamin C deficiency-induced brain injury [16], preventing chronic allograft nephropathy after renal transplantation [17], and ameliorating cognitive defects in senescence-accelerated mice [9] and a Parkinson’s disease model [7]. In human studies, consumption of hydrogen-rich water prevented adult-onset diabetes and insulin resistance [11], as well as oxidative stress in potential metabolic syndrome [8].

Radiotherapy is associated with an increase in ROS, followed by damage to DNA, lipids, and proteins, and activation of transcription factors and signal transduction pathways. It has been estimated that 60-70% of the ionizing radiation-induced cellular damage is caused by hydroxyl radicals [18]. Therefore, a number of trials with the goal of reducing adverse effects due to excess ROS production have been performed with antioxidants delivered during the course of radiotherapy. Supplementation with α-tocopherol improves the salivary flow rate and maintains salivary parameters [19]. Treatment with the antioxidant enzyme superoxide dismutase prevented radiotherapy-induced cystitis and rectitis in bladder cancer patients receiving radiotherapy [20]. In addition, the combined use of pentoxifylline and vitamin E reduced radiation-induced lung fibrosis in patients with lung cancer receiving radiotherapy [21]. Thus, in general, supplementation with antioxidants is likely to offer overall benefits in the treatment of adverse effects of radiotherapy. However, not all antioxidants can afford radioprotection [22, 23, 24]. Furthermore, of significant concern is the finding that high doses of antioxidants administered as adjuvant therapy might compromise the efficacy of radiation treatment and increase of the risk of local recurrence of cancer [25, 26]. Hence, the relatively lower toxicity associated with the use of these antioxidant agents is appealing, but not at the cost of poor tumor control. In contrast, in this study, drinking hydrogen-rich water did not affect radiotherapy’s anti-tumor effects. Our results may suggest that hydrogen water functions not only as an antioxidant, but also plays a protective role by inducing radioprotective hormones or enzymes. Although further studies are warranted to elucidate the safety of hydrogen-rich water and determine the optimal concentration of hydrogen in drinking water, as well as involved mechanisms, daily intake of hydrogen-rich water may be a promising approach for counteracting radiation-induced impairments to QOL. This therapeutic use of hydrogen is also supported by the work of Qian et al., who demonstrated that treating human lymphocyte AHH-1 cells with hydrogen before irradiation significantly inhibited ionizing irradiation-induced apoptosis and increased cell viability in vitro. They also showed that injection of hydrogen-rich saline could protect the gastrointestinal endothelia from radiation-induced injury, decrease plasma malondialdehyde and intestinal 8-hydroxydeoxyguanosine levels, and increase plasma endogenous antioxidants in vivo [27].

In conclusion, our study demonstrated that drinking hydrogen-rich water improved QOL and reduced oxidative markers in patients receiving radiotherapy for liver tumors. This novel approach of oral intake of hydrogen-rich water may be applicable to a wide range of radiation-related adverse symptoms.