Article

Risk of breast cancer after night- and shift work: current evidence and ongoing studies in Denmark.

Institute of Cancer Epidemiology, Danish Cancer Society, Strandboulevarden 49, DK-2100, Copenhagen, Denmark.
Cancer Causes and Control (Impact Factor: 2.96). 06/2006; 17(4):531-7. DOI: 10.1007/s10552-005-9006-5
Source: PubMed

ABSTRACT Breast cancer is the most frequent cancer among women, and the number is increasing worldwide. This tumour is strongly associated with Western lifestyle, but the specific risk factors behind this observation are not well known. Exposure to light-at-night, including disturbance of the circadian rhythm, possibly mediated via the melatonin synthesis and clock genes, has been suggested as a contributing cause of breast cancer. Since shift- and night-time work is prevalent and increasing in modern societies, this exposure may be of public health concern, and contribute to the continuing elevation in breast cancer risk. Until now only few epidemiological studies have evaluated breast cancer risk after shift and night work. Although these studies are all suffering from methodological problems, especially concerning assessment of light exposure, results have consistently shown an increase in risk associated with night and shift work. Good opportunities for epidemiological cancer research exist in Denmark, and several studies on different aspects of breast cancer, work schedules, light exposure and melatonin levels are ongoing in order to further examine different aspects of this issue.

Full-text

Available from: Johnni Hansen, Mar 28, 2014
2 Bookmarks
 · 
103 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Objective: Efficient treatments to phase-advance human circadian rhythms are needed to attenuate circadian misalignment and the associated negative health outcomes that accompany early-morning shift work, early school start times, jet lag, and delayed sleep phase disorder. This study compared three morning bright-light exposure patterns from a single light box (to mimic home treatment) in combination with afternoon melatonin. Methods: Fifty adults (27 males) aged 25.9 ± 5.1 years participated. Sleep/dark was advanced 1 h/day for three treatment days. Participants took 0.5 mg of melatonin 5 h before the baseline bedtime on treatment day 1, and an hour earlier each treatment day. They were exposed to one of three bright-light (~5000 lux) patterns upon waking each morning: four 30-min exposures separated by 30 min of room light (2-h group), four 15-min exposures separated by 45 min of room light (1-h group), and one 30-min exposure (0.5-h group). Dim-light melatonin onsets (DLMOs) before and after treatment determined the phase advance. Results: Compared to the 2-h group (phase shift = 2.4 ± 0.8 h), smaller phase-advance shifts were seen in the 1-h (1.7 ± 0.7 h) and 0.5-h (1.8 ± 0.8 h) groups. The 2-h pattern produced the largest phase advance; however, the single 30-min bright-light exposure was as effective as 1 h of bright light spread over 3.25 h, and it produced 75% of the phase shift observed with 2 h of bright light. Conclusions: A 30-min morning bright-light exposure with afternoon melatonin is an efficient treatment to phase-advance human circadian rhythms.
    Sleep Medicine 12/2014; DOI:10.1016/j.sleep.2014.12.004 · 3.10 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Despite the increasing prevalence of breast cancer, there is no standardized protocol for the follow-up of breast cancer survivors. The Spanish Society of Senology and Breast Disease has supported a consensus document on the follow-up of breast cancer survivors, aimed at patients diagnosed with stage i to iii disease and with invasive and intraepithelial (in situ) lesions, and treated with curative intent, after completion of the initial treatment. Practitioners from all over Spain, with different specialities and areas of activity, participated in the drafting in the document. It was presented at the First Spanish Breast Congress (Primer Congreso Español de la Mama), which took place in October 2013, for the Society's approval. Input from the audience was considered. The main aim of follow-up is the early detection of local and distant recurrences, of new primaries, and evaluation of the adverse effects of the therapies applied. Follow-up should also include psychological support, education on healthy habits, rehabilitation, and social and work reintegration. No significant differences between minimalistic and intensive follow-up have been reported regarding recurrence, overall survival, and quality of life. The length, intervals, and intensity of follow-up should be tailored according to each patient's individual risk of relapse and molecular subtype. This consensus document has the support and endorsement of other scientific societies related to breast disease and present at the congress.
    12/2014; 28(1). DOI:10.1016/j.senol.2014.07.004
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Although the evidence linking exposure to light at night (LAN) and breast cancer risk continues to accumulate, the molecular mechanisms driving this association remain to be fully elucidated. We have previously suggested that long-term exposure to LAN through shiftwork may result in dysregulated patterns of methylation genome-wide. In this study, we investigate the link between miR-34b, a miRNA suggested to be an important tumor suppressor, and shiftwork-related breast cancer. Methylation states in the miR-34b promoter region were previously compared between 10 female long-term shiftworkers and 10 folate intake- and age-matched female dayworkers participating in the Danish "Diet, Cancer and Health" prospective cohort study. In order to further explore the functional role of miR-34b in breast tumorigenesis, a genome-wide expression microarray was carried out in miR-34b-overexpressed MCF-7 breast cancer cells and the identified transcripts were further analyzed for network and functional interrelatedness using Ingenuity Pathway Analysis software. We observed a 49.1 % increase in miR-34b promoter methylation among shiftworkers at a CpG site in this region (p = 0.016). Transfection of the miR-34b mimic in an MCF-7 breast cancer cell line induced differential expression of 230 transcripts that are involved in the interferon-mediated antiviral response as well as apoptotic and antiproliferative gene networks. Together, our results suggest that long-term shiftwork may increase the risk of breast cancer via methylation-based suppression of miR-34b and a consequent reduction in immunomediated anti-tumor capacity and support our previous findings that LAN may induce epigenetic alteration of cancer-relevant microRNAs.
    Cancer Causes and Control 11/2014; 26(2). DOI:10.1007/s10552-014-0494-z · 2.96 Impact Factor