Factors affecting age of onset of menopause and determination of quality of life in menopause

Menopause is a process in the climacteric period, characterized by a reduction in ovarian activity, a fall in the fertility rate, and a range of symptoms including irregular menstruation intervals. Most women enter menopause in their 40s, but this can vary from one individual to another. Although there are many factors affecting the age of menopause onset, there is no general agreement on them. Studies have shown many factors to affect the age of menopause, such as the mother’s age at menopause, the age at menarche, gestational age, use of oral contraceptives, irregular menstrual cycle, number of pregnancies, body mass index, use of tobacco and alcohol, physical activity, unilateral oophorectomy, serum lead levels, consumption of polyunsaturated fat, socioeconomic status and educational level. During this period, hormonal and biochemical changes give rise to various symptoms in the woman’s body. In menopause period, physical, psychological, social and sexual changes have a negative effect on quality of life in women. Recently, different measures have been used to assess women’s quality of life in this period of change. The purpose of this review was to examine the factors affecting the onset age of menopause and the measures of quality of life related to menopause.


Introduction
Scientific and technological advances have lengthened the span of life and led to an increase in world's elderly population. While in 1000 B.C., average life expectancy for women is estimated to have been 28 years of age, today this figure has reached to 8 th decade of life (1) . According to 2013 world population data, life expectancy for newborn girls is 73 years in average around the world and 78 in Turkey (2) . The report of the Menopause and Osteoporosis Association of Turkey, published in 2002, reveals that the average age of menopause is 47 (3) . Accordingly, it can be said that a woman who is expected to live 78 years spends a significant part of her life in menopause.
The word "menopause" derives from the Greek "men" (month or monthly cycle) and "pausis" (end, stop), i.e., "the cessation of monthly cycle." The World Health Organization (WHO) describes it as the permanent cessation of menstruation as a result of the loss of ovarian follicular function (4,5) . The menopause signals are a reduction of ovarian activity and a fall in fertility. With the appearance of various symptoms and irregular menstrual periods, it is a characteristic phase of the climacteric stage. The hormonal and biochemical changes that occur in this period lead to various symptoms in woman's body (6) .

The Onset Age of Menopause and Influencing Factors
The transition from a woman's fertile period to the period in which the ovaries begin to lose their function is achieved gradually. It is for this reason that it is difficult to set down a definite age at which menopause will begin for every woman. This period generally commences in the fourth decade of life and varies from one woman to another. Community-based studies indicate that the distribution of menopausal age displays a bell curve that ranges from age 40, ending around the age of 54, generally clustering around the ages 45-55 (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)19,(21)(22)(23)(24)(25) . In one study, the average age of menopause has been reported as 54 in Europe, 51.4 in North America, 48.6 in Latin America and 51.1 in Asia (20) . Although there are many factors that influence the onset of menopause, there is no consensus as to whether these factors are definitive in all women (Table 1). Studies show that the onset age of menopause is affected by the age at the first menstrual period, the use of oral contraceptives, the number of pregnancies experienced, Body Mass Index (BMI), smoking, drinking alcoholic beverages, physical activity, blood lead levels and other factors (26)(27)(28)(29)(30)(31)(32)(33)(34) . It is believed that in about 50% of women, genetic factors play a role in determining the age of onset of menopause (26) . Women whose mothers entered menopause at an early age are at a high risk of early onset menopause (27) . In many studies, it has been shown that women who smoke enter menopause at earlier ages than non-smokers (30)(31)(32)(33)(35)(36)(37)(38) . It has been observed that women who smoke 14 or more cigarettes a day enter menopause 2.8 years earlier than women who do not smoke (39) . Women who do not drink alcoholic beverages have been found to enter menopause at earlier ages than women who do consume alcoholic drinks (31,33,37,38) . While heavy physical activity is associated with early menopause (19,33) , light physical activity delays menopause to later ages (31,40) . A high consumption of polyunsaturated fats accelerates the onset of menopause while a high consumption of total calories, fruits and protein delays it (32,33) . A high BMI has been found to be associated with a higher menopause onset age (19,28,30,31,38,41,42) . It has been found that women with hypertension and a low exposure to the sun throughout the life enter menopause at earlier ages (19) .
An association has been found between life-long irregular menstrual cycles and a later menopause (30) . An early menarche has been associated with early menopause (27)(28)(29)(30) . Nulliparity has been associated with early menopause (28,41,43) , while multiparity is related to late menopause (18,19,30) . Having the first pregnancy at a later age has been associated with a later menopause onset (32) . The use of oral contraceptives has been associated with late menopause (19,29,31,37) . Women who undergo an unilateral oophorectomy (average age=49.6 years) have been found to enter menopause at an earlier age than women who have not had the procedure (average age=50.7 years) (42) . A high serum ferritin level and a low bone mineral density may be the causes of early menopause (44) . An association has been found between onset age of menopause and bone lead levels and longterm exposure to lead (unrelated to professional reasons). According to tibia measurement results, it has been found that women with high lead levels enter menopause 1.21 years earlier than women with low levels (34) . Women with arsenic skin lesions have been observed to enter menopause 1.5 years earlier than women who do not have such lesions. It has been seen that women who are intensely exposed to arsenic experience menopause 2 years earlier than women who have never been exposed or who have been less exposed (45) . Low socioeconomic status has been associated with early menopause (26,28) . Women with a lower level of education have been found to enter menopause at earlier ages than women with higher levels of education (26)(27)(28)31,41,43) . Onset age of menopause is defined as "early menopause" when menopause commences before the age of 40 (20,46) . Studies show that the quality of life of women who enter menopause at early ages is more adversely affected (28,46,47) .

A Determination of Quality of Life of Women in Menopausal Period
The concept of quality of life is defined as the perception of the individual about his/her situation in life in the context of the framework of that individual's culture and value systems, goals, expectations, standards and interests. Influenced by a complex number of factors, such as an individual's physical health, psychological status, beliefs, social relations and environment, quality of life is used as an important measurement in assessing health status and the effects of therapies (48) . In later adult years, the quality of life of women may be adversely affected by the physical and mental changes that may come about in the menopausal transition (49) . Quality of life in menopause is related to the degree to which a woman is able to cope with the changes and symptoms appearing in her body with the onset of menopause and her sense of   (50) . The menopausal transition is associated with physical and mental changes in a woman's life that can have an impact on her health (51) . Studies show that the physical, psychological, social and sexual changes observed in the menopausal period have a negative effect on women's quality of life (13,14,(51)(52)(53) . Ninety-six percent of women have reported to experience menopause-related symptoms and their quality of life is affected not only physically and psychologically but also socially (54,55) . In particular, women in perimenopause and early postmenopause live through a more negative impact on their quality of life (56) . Much research has been carried out on the effect of menopause on women's quality of life and the relationship between menopause and quality of life continues to be a controversial topic (57) . In recent years, different instruments have been developed and used to assess women's quality of life during the menopausal transition (58) . Each of these menopausal quality of life measuring instruments are of different content and they measure different aspects of life during menopause (56) . Although finding the ideal measuring tool for assessing quality of life is a topic still being explored, existing and accepted instruments in the literature related to menopause and their characteristics are given in Table 2a, 2b, 2c, 2d (56,57,(59)(60)(61)(62)(63)(64)(65) .
Of the menopausal quality of life scales indicated in the table above, the validity and reliability of the Menopausal Rating Scale and the Menopause-Specific QOL Questionnaire have been translated into Turkish and tested in the Turkish population (52,66,67) . The Kupperman Index and the Greene Climacteric Scale are also used in studies in Turkey in the assessment of menopausal symptoms (67)(68)(69)(70)(71) . The Turkish validity and reliability studies of these two scales, however, could not be found in the literature.

Conclusion
As life expectancy increases, so does the time spent in the period of menopause. Women are subjected to the hormonal and biochemical changes that adversely affect their quality of life in this period. Menopause-specific quality of life scales seek to identify and measure the severity of the menopausal symptoms women experience in order to define quality of life during menopause.
The quality of life of women entering menopause at earlier ages is thought be more adversely affected. Ensuring a high quality of life for women in menopause may only be made possible by defining the extent of their quality of life and the factors related to this.