Circadian rhythm and time-of-day-effects of (anti)oxidant biomarkers for epidemiological studies.

Various biomarkers of oxidative stress and redox status have been used in a number of clinical and epidemiological studies related to diseases and conditions that involve disturbances of the redox balance. However, a comprehensive study of diurnal variations of a set of biomarkers has not been conducted so far. Therefore, the aim of this study is to investigate circadian rhythm and time-of-day-effects of a set of frequently used biomarkers of oxidative stress, redox and antioxidant status in serum/plasma. These biomarkers include Reactive Oxygen Metabolites (ROM), Biological Antioxidant Potency (BAP), Total Thiols in Proteins (TTP), high-sensitive C-Reactive Protein (CRP) and Uric Acid (UA). During a 24-hr study, blood sampling was conducted 6 times at 4-hr intervals. The presence of circadian rhythm was analyzed with CircWave analysis, whereas the effect of time was analyzed with Repeated Measures ANOVA (RM-ANOVA). Thereby, the main focus was on the time points in working hours (8, 12 and 16 hr), which are used frequently in practice. Of all investigated biomarkers, only TTP in males demonstrated statistically significant circadian rhythm (p = 0.040). A statistically significant effect between all six time points with RM-ANOVA was observed for ROM, TTP and UA in both genders, and for BAP in females only. No statistically significant differences were observed between the time points 8 hr and 12 hr for any of the biomarkers that were assessed in our study. In conclusion, diurnal variations in some of the studied biomarkers that we demonstrate here should be taken into account when designing and conducting clinical and epidemiological studies. It is advised to standardize the time of sampling with a preference in the morning hours.

Diurnal Variation of Hormonal and Lipid Biomarkers in a Molecular Epidemiology-Like Setting.

INTRODUCTION: Many molecular epidemiology studies focusing on high prevalent diseases, such as metabolic disorders and cancer, investigate metabolic and hormonal markers. In general, sampling for these markers can occur at any time-point during the day or after an overnight fast. However, environmental factors, such as light exposure and food intake might affect the levels of these markers, since they provide input for the internal time-keeping system. When diurnal variation is larger than the inter-individual variation, time of day should be taken into account. Importantly, heterogeneity in diurnal variation and disturbance of circadian rhythms among a study population might increasingly occur as a result of our increasing 24/7 economy and related variation in exposure to environmental factors (such as light and food). AIM: The aim of the present study was to determine whether a set of often used biomarkers shows diurnal variation in a setting resembling large molecular epidemiology studies, i.e., non-fasted and limited control possibilities for other environmental influences. RESULTS: We show that markers for which diurnal variation is not an issue are adrenocorticotropic hormone, follicle stimulating hormone, estradiol and high-density lipoprotein. For all other tested markers diurnal variation was observed in at least one gender (cholesterol, cortisol, dehydroepiandrosterone sulfate, free fatty acids, low-density lipoprotein, luteinizing hormone, prolactin, progesterone, testosterone, triglycerides, total triiodothyronine and thyroid-stimulating hormone) or could not reliably be detected (human growth hormone). DISCUSSION: Thus, studies investigating these markers should take diurnal variation into account, for which we provide some options. Furthermore, our study indicates the need for investigating diurnal variation (in literature or experimentally) before setting up studies measuring markers in routine and controlled settings, especially since time-of-day likely matters for many more markers than the ones investigated in the present study.

Recommendations for the prevention of breast cancer in shift workers.

The functioning of the human body is regulated by the rhythmical change between rest and activity. The SCN (suprachiasmatic nucleus) is responsible for the central control of the biorhythm and the genetic prediction of the individual chronotype, whereas peripheral time cues such as light, social contacts and times of meals modulate the rhythmical activity of the body. Shift workers suffer from a disruption of the sleep-wake rhythm, insomnia and a lack of melatonin. These factors might trigger the development of breast cancer in female shift workers. The growing amount of data which indicate the high risk of breast cancer in female shift workers demonstrates the need for the implementation of prevention strategies against insomnia in shift workers. These strategies include regular sleep education courses on the prevention of sleep disorders in companies. The individual chronotype could be an important predictor for the adaptability to shift work.

Health Organization in Republic of Macedonia-the place of preventive health care in the medical health system: advantages and disadvantages.

The health system in Macedonia is organized by public or private property health institutions divided on three levels: primary, secondary and tertiary health care. According to the legal regulations and their acts, regulatory authorities for preventive care are the health institutions of primary health care (whether they have private or public character), heath care establishments and some of the hospitals. In the period of transition starting from 1991 up to this day, numerous health system modifications have been made concerning health reforms: common alterations in health legislation change in property of health institutions, realignment of authorities etc. The adjustment of the system to the new circumstances and constant changes has provoked partial disruption in the established system for preventive health care activity.