To the best of our knowledge, this is the first study using 4-year longitudinal data to compare the changes in characteristics of TCM constitutions and the factors influencing the development of TCMC types over time. The main findings:
(1) A majority (83.14%) of the participants in this study aged over 45 and most of them suffering chronic diseases or dysfunction dystrophic diseases for a long time on or before baseline to the 4-year follow-up and data revealed the percentage of participants having unbalanced and more complex TCMC types in follow-up was higher than that of baseline. The aging population is expected to more obvious in Hong Kong in near future. A local survey has shown that 75% of local people aged 65 or over, and 45% of people aged 45 to 64 are suffering from one or more chronic diseases [16, 17]. The elderly healthcare issues are a big challenge for every government since the elderly are less healthy than the youth and therefore increased the government spending on their health care and has great impacts on the government’s resources [18, 19]. “Treating disease before its onset” is the core theory of TCM in preventive diseases before occurrences. TCM theory focuses on strengthening the body's healthy qi to prevent diseases before occurrence through improving the balance of yin and yang [20]. Hence, it recommends that individuals should improve their health based on one’s TCMCs assessments and through changing acquired factors such as lifestyle, dietary habit, and emotional status, etc. Therefore, using a TCM regimen to protect health and prevent aging is one of the effective health defenses for chronic diseases in an elderly population.
(2) The findings of this study proved that the distributions of TCMC types are both relatively stable and adjustable which accordant to that of developing acquired factors and changed the individual’s constitutions over time. On one hand, QDF, PD, and PW constitutions were still the top three frequent unbalanced TCMC types at baseline and follow-up. However, ND, BS, and QDP constitutions are substantially increased in women and suffered during menopause. Firstly, most of the participants’ acquired factors such as social-demographic, living environment, and lifestyle haven’t changed that accounted for the consistency with some TCMCs types in the follow-up. The development of the QDF constitution is closely related to the lifestyle of Hong Kong dwellers’ that caused the high pressure from work and living cost, lack of sleep, and fast-paced lifestyle resulting in damage to the healthy Qi. Similarly, suffering negative emotion might also a risk factor of formation of QDF constitution during the follow-up as well as unhappy emotion at baseline. Qi-deficiency always accompanies a morbid state characterized by unsmooth flow and obstruction of qi, which results in Qi-depression constitution, blockage of phlegm, dampness, and stagnant blood [21, 22]. These are accordant with the theory of all diseases that are born from Qi in the earliest and classic TCM book The Yellow Emperor’s Inner Classic [23, 24]. The lifestyle of prolonged consumption of cold drinks, awaken at night time, and misusing cold air conditioners throughout the year are the key factors for the development of the Yang-deficiency constitution [2]. The prevalence of the Phlegm-wetness constitution is higher among the participants because Hong Kong is a city locates in the South China Sea and belongs to a subtropical zone with climate characteristics of hot-wet-damp. Secondly, the explanation for the remarkable increase of ND, BS, and QDP constitutions could be related to that most of the participants are suffering in the menopause stage during the follow-up period. Menopause is defined as the time in most women's lives that occurs between 49 and 52 years old when their menstrual periods stop permanently due to the natural depletion of ovarian oocytes [25, 26]. The diagnosis is typically made retrospectively after the woman has missed menses for 12 consecutive months. During this time, women often experience menopausal syndrome including the symptoms of hot flashes, sweating, and reddening of the skin, vaginal dryness, trouble sleeping, and mood changes [27, 28]. Clinical epidemiological studies found that Yin-deficiency, Blood-stasis, and Qi-depressed constitutions were the dominant unbalanced TCMC types in the women who were around menopause [29]. From The Yellow Emperor’s Inner Classic, women who suffering menopause are mostly under the "seven-seven years" (at 49 years old) with the Physiological features of kidney fading, Chong-Ren deficiency and heavenly tenth (Tian Kui Chinese) deficiency resulted in liver-kidney depletion [30]. “Yin-Blood is the root of woman and liver is the congenital root of woman for blood storage” [31]. The primary physiological function of the liver is free coursing. It ensures the free movement of qi and prevents qi stagnation and its function, which is based on the abundance of yin-blood [32]. Losing free coursing of the liver generally causes disharmony of the qi and blood ensues the development of blood stasis [33]. In other words, menopausal women are more prone to have unbalanced TCMC types, including, ND, QDP, and BS constitutions, and develop the high menopausal syndrome. Hence, the proper adjustment and good health can help soothing or avoid suffering menopausal symptoms and reduce the discomfort during the period.
(3) Health status was found as one of the most significant influencing factors for the development of TCMC types in both baseline and follow-up. According to TCM theory, Unbalanced TCMC types often damage physical and/or mental health even in the situation diagnosed with “no disease” in western medicines [2, 4]. The unbalanced constitutions naturally cause weak healthy qi that triggers more susceptibility to get diseases. Healthy qi is known as generating from parents (as innate essence) and food (as acquired essence) [1], and TCMCs are the comprehensive manifestations of the function of healthy qi [19]. In the follow-up, it has been recognized that participants who suffer from chronic diseases that can damage the healthy qi due to imbalanced of yin and yang resulted in unbalanced TCMCs. Furthermore, in the follow-up, the total number of unbalanced TCMC types owned by one person has increased (more complex TCMC types) that indicates TCMC types could be developed by an individual’s health status. It is confirmed that the development of the disease can be influenced by TCMC types, which eventually change TCMC types. Earlier, a pilot study recruited 218 participants with hepatic disease resulting in phlegm and dampness in the meridian during the early stage. Thus, the constitution eventually alters into the different types of constitutions, ensuing Phlegm-wetness, Qi-deficiency, or Wetness-heat [34]. Su wen (Plain Questions) pointed out “the sufficient healthy qi is maintained endogenously, thus the body is not easy to be suffered by evil qi”. Hence, the best way to preventing unbalanced TCMC types and diseases is to avoid contacting evil qi and maintaining the balance between yin and yang and regulate the constitution.
(4) Whether aging is a protective factor for unbalanced TCMC types still controversial. The data of baseline and follow-up preferred to support the aging that is a protective factor for the formation of Qi-deficiency, Yang-deficiency, blood stasis, and Qi-depressed and wetness-heat constitutions. Findings of two large studies involving 2043 and 8448 subjects showed there was no significant difference between elderly and younger people with the Phlegm-wetness constitution [35, 36]. However, a study with a 2168 sample size found that the unbalanced TCMC types of Qi-deficiency, Phlegm-wetness and blood-stasis, and Yang-deficiency among elderly people were higher than younger people [37]. Enjoying a leisure life during retirement or a part-time job with proper manual working without suffering from high working pressures would reduce the consumption of qi-blood and keep the balance of Yin-Yang especially in the elderly population. Overstrain is easy to harm the physical body and consume qi-blood to cause essence-qi shortage thus develop unbalanced TCMC types [2]. A study analyzed data from a random sample of 1,546 people from ages 21 to 99 through a phone interview and filled out the questionnaire indicated that happiness and wellbeing are a U-shaped curve in the entire life, dipping down in middle age and inching up in older age [38]. The outcomes of this study are also consistent with this conclusion that participants suffered less unhappy emotion as they are aged, which would avoid liver-qi stagnation thus reducing some unbalanced TCMC occurrence. However, more researches are highly required to prove that aging is a protective factor of TCMC types.
(5) Emotional status found as a core factor influencing the development of TCMC types during the 4-year follow-up. Firstly, this study found the unhappy emotion and suffering negative effect on body-mind health that were risk factors for the formations of QDF, BD, QDP constitutions, and risk factor of more complex unbalanced TCMC types. Emotions can be defined as a positive or negative experience that is associated with a particular pattern of physiological activity as well as responses to significant internal and external events [39]. Emotional states are closely related to qi-blood, the yin-yang of the organs according to TCM theory. With consistent with the recognition of the book The Yellow Emperor’s Inner Classic pointed out a negative effect on body-mind health that can consume Yin-blood secretly and gradually affecting a qi-blood variety of the viscera and most likely to form Qi-deficiency and Qi-depressed constitutions [23]. Our findings also confirmed that frequent emotional fluctuation could harm body-mind health most likely resulted in Qi-depressed constitution with high frequency paired with Qi-deficiency constitution owned by the individual. Qi-deficiency and depression can accumulate heart/liver to cause fire, as well as impaired Yin-consume the body fluid then leading to Yang heat diathesis or Yin deficiency diathesis. Qi stagnation can produce the blood-stasis constitution [40, 41]. Thus, Good mental status, conscious activities, and stable emotion are beneficial to the health, ensuing to prevent the disorder of qi movement that helps to avoid unbalanced TCMC types’ occurrence.
(6) Lifestyle factors such as physical exercise or dietary habits play very important roles in the development of TCMC types over time. Lifestyle factor refers to the behavioral style such as food, daily life at home, work, hobby, physical exercise, etc. Proper daily activities would be beneficial to reduce the harmfulness to health [20, 35]. Proper physical exercise can move qi and blood that enhance the visceral function to more powerful and more healthy [7]. On the other hand, extreme and fewer exercises may weaken the circulation of qi-blood muscles to be flabby, and spleen-stomach dysfunction, thus the development of fat and damp-greasy constitution. This follow-up study re-confirmed that regular exercise is a protector of the wetness-heat constitution but not as for QDF, PD, and BS constitutions. Duration of the exercise and different kinds of physical exercise should be considered to affect the TCMC types. Hence, duration and types of physical exercises should be further investigated by individuals in forming TCMC types. Dietary habit may also be a contributory factor influenced TCMC types. All the participants had received TCM regimen dietary according to their diagnosed TCMC types to improve their health by individuals at the baseline, but the rate of the participants followed these regimen was low and duration was short thus there was no significant difference in the TCMC types. Experts in different dynasties had paid much attention to the relationship between diet and good health. One of the well-known experts of Sun SiMao, a distinguished Taoist priest, and an expert of Chinese medicine in the Tang Dynasty pointed out that “The foundation of the settlement lies based on the food and how people take in” and “those who do not know to eat, then they are unfit to live” [42], hence, the diet is bare necessities of life and a guarantee of good health and long life. A follow-up has also observed that the habit of using regular TCM is a protector for keeping participants in normality constitution when compared with others in unbalanced TCMC types. On the other hand, those participants in the poorer health status of those diagnosed with Yang-deficiency, Qi-deficiency, or Phlegm-wetness constitutions or with more complexed unbalanced TCMC types tended to use TCM to improve their health. Today, most of the Hong Kong dwellers accept TCM medications and prefer to choose them for promoting chronic diseases such as dampness, qi-yin deficiency, or even as alternative meditations for cancer patients to reduce side effects or improve the quality of life [16, 17, 19, 43, 44]. We take into account and found that more complex unbalanced TCMC types reflected the poorer health status and usage of Chinese medicines aided to manage their unbalanced TCMC as alternative medications. However, the regular consumption of a healthy diet and TCM regimen for a longer time is needed to observe its effect on managing an individual’s unbalanced TCMC that is now underway.