Winter: Seasonality in Humans

Introduction

The evidence of seasonality in humans is limited. Whether human exhibit seasonality or not remains an open question that this paper is going to handle. It has been demonstrated by epidemiological studies over time. This paper is also going to focus on critical review of evidences supporting seasonality in humans. It is also going to provide what studies and research have shown. It has also identified the limitations to this study as well making a plan of work that comprises of a hypothesis, study design, and analysis of data.

Discussion

Seasonality in humans

Seasonality in distribution of humans has been demonstrated consistently by epidemiological studies in a number of geographical areas. A possible hypothesis suggested explaining this seasonality. Despite seasonal effect on reproduction being well-documented and broadly investigated in mammals, there is still limited information concerning the influence of seasonality and its mechanisms on primates and human. According to Bobak (16) research has shown that there is the deterioration of sperm quality during summers especially in the sub equatorial regions which is likely to reduce conception levels resulting to a decrease in the rate of births during spring. Science explains this aspect vaguely limiting the knowledge of seasonality that occurs in human.

There is an exhibit of seasonal variations in almost all human populations in terms of birth rates. The cases of this seasonality among human is poorly understood. It could be purely because of seasonal marriages, cultural aspects as well as religious aspects. Miura (50). Alternatively, my review paper focuses on environmental aspects such as photoperiod; nutrition and temperature contribute to reproduction variations, factors that many have used to explain seasonal variations. Lumaa (49). The variations exist in the rates of births and conception. Human have the ability produce continuously unless inhibited by environmental factors. First it is evident that human population is deprived in environments where individuals have limited food tend to spend more of their energy looking for food which in turn delay and suppress the frequency of ovulation. This is common in tropical areas where they depend on rain for food. This causes seasonal variations. Areas which experience high temperatures also suppress ovulation and the survival of the embryo; this is directly connected to the human reproductive axis It also affects spermatogenesis. Lerchl (3). The areas mentioned are unevenly distributed around the world hence seasonality is not commonly expressed among human, it is only a few who are subjected to it. They have no control over nature.

It is true that seasonality exists among all populations but then when we look at an aspect like sexual orientation the idea changes. Genetic research has shown that genes influence sexual orientation but molecular research is yet to state the specific type of genes that influence sexual orientation. Roenneberg (220). It is evident that seasonality cannot exist among lesbians and homosexuals because there is no conception because both parties are of the same sex.

Does human immune system affect seasonality? Well, by looking at winter seasons, which are very cold, people, are more susceptible to diseases like flu lowering their immune system. According to Rojansky (11) people are more susceptible in winter as compared to other seasons like summer. When people are unhealthy, conception rates are reduced lowering birth rates in return (12). This is what is termed as seasonality in humans. Nevertheless, we cannot say that immune system is a major aspect in seasonality because many people are healthy and matters to do with immunity in relation to seasonality are insignificant.

According to Bobak (19) reproduction is a major aspect of seasonality. Babies of seasonal breeders are born in spring; for example lamb. There are warm temperatures during spring and also there is more food availability in summer. This form of reproduction is timed because it is evident that the baby will survive (20). But when hamster is fertile it is different because gestation period is shorter. So working backwards from spring, depending on gestation period, it is when animals are most fertile to be able to conceive. A sheep is called a long day breeder because it is fertile. Sheep and deer are more fertile in autumn because the off springs will be born in spring. Roenneberg (17). Animals that breed during summer and spring are known as long-day breeders while breeding during fall are short-day breeders. Thyroid hormone regulates seasonal breeding in animals.

Limitations

Seasonality in photo periods has an impact on mood variations in human, the bases of brain seasonality in human cognitions still elusive. According to Solomon (48) the limitation evident in this is lack of enough evidence to support this study due to the fact that human brain activities in seasonal rhythms are difficult to measure. Many factors affect the normal functioning of the brain (49). These factors include; sleep and wake rhythm, exposure to light, physical exercise, and food and temperature variations (50).

The evidence of seasonality in humans is limited. Whether humans exhibit seasonality or not is an open question. There is limited knowledge concerning the influence of seasonality and its mechanism on human and primates.

Study Design

I have decided to come up with a study design that will investigate annual rhythms on human brain function in cross sectional study design of young and healthy individuals. The study is supposed to be carried out in the laboratory under strict and controlled conditions. The aim of this experiment is to determine whether physiological and behavioural variables could give an account for the noted yearly variations in brain responses of human with a primary goal of assessing how the neural correlates with the two assigned tasks in during the investigation. Stowlwijk (7).

My plan of work begins with enrolling two individuals in a timely manner such that the assessment can span through all the four seasons. Annual neural responses variations assessment is at the end of the study design. Wallner (60). The individuals are to be retained in a free seasonal cases environment for a maximum of 5 days following their normal routine of sleep and wake. Why are the individual to be retained in such an environment for 5 days and what are the brain responses after the 5 days? This study design aims at answering these questions. My hypothesis for this study design is that all the 5 days of experiment are carried out under controlled conditions, and the two brain tasks are to undergo seasonality

Functional MRI from the two individuals were acquired daily after 1 hour from sleep. After the 5 days, their brain responses will be assessed using (fMRI) functional magnetic resonance imaging. Two unlike cognitive tasks are undertaken. It will be discovered that the replication of seasonal changes in melatonin secretion is not possible. Long 5 days of no exposure to the normal affect secretion of melatonin rhythms in human species. According to Rojansky (10) human melatonin time-period secretions and sleep respond to the variations in the photoperiods.

The PVT brain responses are associated to the photoperiods with which the two individuals are exposed. From the results obtained from the fMRI the individuals will not have seen light for 2 days; this was during the sleeping hours. Jongbloet (6). The individuals are supposed to follow their normal daily routine starting from day 2 so that their normal functioning of the body can be collected. Melatonin is measured rapid and directly using antibodies and iodinated tracer in saliva. Endogenous Melatonin plays important roles in the human body. They are the messengers of the body, change in duration of melatonin, changes according to photoperiod, convey information about day length and contract and expand of melatonin depending on melatonin.

From the data analysis point of view the results obtained will show that the brain responses of these individuals vary across all seasons with annual rhythm phases being different. Both the brain responses of these individuals will vary across all seasons. Minimum and maximum responses are detected in winter and summer for sustained attention tasks respectively. Minimum maximum responses in memory working tasks are detected during spring and autumn respectively. In general, the findings will reveal unappreciated seasonality phases in human cognitive brain activity. Cummings (60). It is one of the main contributors to seasonality in reproduction among human. It is an effective mechanism that can be used to lower birth rate in vulnerable populations.

Environmental daily changes have shaped life on earth. Similarly, seasonal variation have corresponded to yearly environmental changes to which over time, organisms have adapted. However, as stated earlier, there is limited evidence of seasonality among human species. According to Xaquin (5) circadian cycles are notable in almost all living organisms not to forget cognition and human psychology. Variations in the environmental seasons have caused annual adaptations (6). This is evident in many species. Nevertheless, seasonality seems very much limited in species or they are less recognized.

Conclusion

This paper has handled seasonality in humans broadly. The limitations of this knowledge as well as study designs have been handled. The paper has critically reviewed the evidences supporting seasonality in humans and also designing a study design whose aims and analysis are explicit.

Reference List

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