Current problems of food intake in young women in Japan: Their influence on female reproductive function

Abstract

Accumulating evidence suggests that food customs are associated with quality of life in women of the reproductive age. In Japan, dietary limitation for cosmetic purposes, skipping food intake, intake of processed foods and the shift from Japanese to Westernized style food have increased among young women. These changes in food habits can cause inadequate intake of calories, micronutrients, unsaturated fat, phytestrogens and fiber as well as increasing environmental toxins. Furthermore, these food habits increase risk as a result of intake of food additives, anti‐oxidants, processing agents and sweeteners, which have been demonstrated to be harmful to human health. These factors are speculated to not only influence the present lifestyle, but also to induce gynecologic disorders such as dysmenorrhea and irregular menstruation. The adverse effects of these dietary habits on pregnancy outcome and carcinogenesis of breast and ovarian cancers have also been demonstrated. In addition, latent development of organic diseases such as endometriosis, which are accompanied by dysmenorrhea, is a concern under the current nutritional environment in young women. Thus, it is an urgent issue to evaluate the present situation of eating habits in young Japanese women and estimate the influence of these habits on the quality of life including reproductive functions. (Reprod Med Biol 2004; 3: 107–114)

INTRODUCTION

IN RECENT YEARS, quality of life (QOL) in women's health has become of great interest worldwide. Dietary habits, sleeping and education are fundamental factors that influence human lifestyles and individual QOL. Among these factors, food habits can affect lifestyle‐related and/or psychological diseases because such habits lead to nutritional excess or deficiency as well as impaired circadian rhythms. ¹ , ² , ³ , ⁴ In addition, the adverse effects of environmental hormones or toxins on human health, which will be manifested in later life, have been emphasized. ⁵ , ⁶ , ⁷ Thus, dietary habits in young women may determine their QOL in subsequent middle or old age and should be evaluated from the perspective of total benefit throughout their whole life.

In Japan, food intake behavior in young women has become considerably diversified. The attention has been paid to the dramatic change in young women from the perspective of QOL in the following reproductive and postmenopausal ages. For example, widespread consumption of fast food, skipping of food intake, and the shift from Japanese to Westernized style foods are increasing among young women in Japan. ⁸ , ⁹ These factors are speculated to influence not only the present lifestyle but also future medical disorders such as cardiovascular and metabolic diseases. ¹⁰ , ¹¹

Accumulating evidence suggests that food customs are associated with QOL in women during reproductive age. ¹² , ¹³ , ¹⁴ Anti‐oxidant agents, estrogenic agents or toxic agents in food have been proposed to lead to malignant diseases of the reproductive organs such as endometrial carcinoma and breast carcinoma. ¹⁵ , ¹⁶ , ¹⁷ Furthermore, menstrual and reproductive factors have also been proposed to be associated with malignant diseases in other organs. ¹⁸ Accordingly, it is important to evaluate the present situation of eating habits in young women and estimate their influence on QOL. In the present review article, we described the current changes in food intake among Japanese young women and discuss their potential problems especially from the perspective of female reproductive functions.

The changes in food intake behaviors/customs and the problems these changes induce in Japanese women

One of the most common nutritional issues among young women in Japan is poor energy intake and/or inappropriate food selection because of dietary limitation for cosmetic purposes, which can result in poor intake of protein, carbohydrate and essential fatty acids along with diet‐related psychological stress. ¹⁹ , ²⁰ In the above situations, the bone‐building micronutrients, such as calcium, vitamins, iron and zinc are estimated to be low. ¹³ Therefore, numerous supplements for these nutrients have become commercially available in Japan and daily intake of these supplements has become popular among young women. However, the majority of these supplements are not medical drugs and little information about contaminating compounds has been provided. The excessive intake of food including confectionary also remains a big problem among young women, causing obesity during adolescence. ²¹ , ²²

Although it has become a custom for Japanese people to consume three meals a day, a considerable number of families do not eat breakfast. ⁸ There are several reports concerning the effects of skipping breakfast on the QOL of the younger generation. ²³ , ²⁴ In Japan, Kunimoto et al. reported that breakfast skipping is significantly related to constipation in working women and signs of this relationship have already appeared in adolescents. ²⁵

Another notable change in food customs among young Japanese people is the increased intake of processed foods commonly sold in convenience stores. ⁸ Many of these foods have relatively long preservation terms. The current expansion of food distribution has demanded strict quality control of food, leading to an excessive use of chemical preservatives in domestically processed food. Thus, considerable amounts of antiseptic are estimated to be present in these foods, but the precise influence on subsequent QOL on young people have not been thoroughly clarified. ⁸ Even regarding fresh food, Japan has been undergoing a continuous reduction in the self‐sufficiency food rate, and there is a risk that imported foods have undergone excessive post‐harvest chemical treatments. ²⁶ , ²⁷

An important point in the shift from Japanese to Westernized style food is an increase in intake of meat and dairy products that are considered related to metabolic diseases and cancer. ²⁸ , ²⁹ , ³⁰ , ³¹ It should also be noted that besides traditional and trusted preservative procedures for meat and dairy products that have been used in Western countries for a long time, ³² Western foods produced in our country, for example sausage and processed cheese, are further processed by modified methods to adapt these products to Japanese tastes. The long‐term effects of these methods developed in Japan should be re‐assessed in the future from the aspect of safety and health. Currently, the packaging methods for processed meat are known to affect food quality and/or safety during the process of sterilizing irradiation. ²³ , ³⁴

Recently, the impaired reproductive status of vegetarians has received attention in Western countries. ³⁵ Although a similar problem may become evident in the future, the current number of vegetarians is not very high among young Japanease women. In contrast to Western countries, in Japan the so‐called fish‐eating population still comprises a major portion of the population. The nutritional differences between fish and meats such as the ratios of unsaturated fatty acids have been documented. In general, domestic animals are treated by antibiotics, ³⁶ , ³⁷ while aquacultured fishes are exposed by antiseptic agents. ³⁸ In wild fishes, environmental toxins such as mercury and dioxins are accumulated over a sequential food chain. ³⁹ , ⁴⁰ Many vegetables are grown under agricultural chemicals then treated by antiseptic agents. ⁴¹

Thus, the environmental conditions of food available to young Japanese women involve various problems. Although the selection of dietary habits is fundamentally based on the individual lifestyle and socioeconomic status, young Japanese women tend to pay little attention to the quality and safety of food, preferring to consider the time and cost factor in food intake, which may increase the risk of unsuitable nutrition and/or exposure to toxic agents.

Dysmenorrhea and irregular menstruation

Primary dysmenorrhea is a common gynecologic disorder in young women. ⁴² It begins within 6–12 months from menarche and is characterized by localized pain in the abdominal inferior quadrants. Dysmenorrhea is caused mainly by hormonal disorders in ovarian function or pelvic organic diseases. ⁴³ Irregular menstruation is also a very common gynecologic symptom in young women. In our previous study, more than the half of female college students aged from 18 to 20 complained of dysmenorrhea and/or irregular menstruation. ⁹ In general, irregular menstruation is caused by dysfunction in the hypothalamic‐pituitary‐ovarian axis. However, primary dysmenorrhea is derived from an abnormal increase in the contractile activity of the uterus. ⁴⁴ It is usually a result of functional immaturity in ovarian sex steroid hormone production that stimulates local production of chemical mediators such as prostaglandins E2 and F2α, and leukotrienes in the uterus during menstruation. ⁴¹ Thus, irregular menstruation and dysmenorrhea are important signs of functional disturbance in the hypothalamic‐pituitary‐ovarian axis and subsequent local inflammation in the pelvic cavity. ⁴² , ⁴³ , ⁴⁴ , ⁴⁵ , ⁴⁶ They are also excellent parameters that reflect female psycho‐physiological status.

Low intake of food and nutritional deficiency

In recent times, some adolescents have become concerned with losing bodyweight. In young Japanese women, more than 60% of college students underwent a diet to lose weight, despite having a normal or low body mass index. ⁹ It was reported that attempting to lose weight is significantly associated with increased frequency of irregular menstruation and dysmenorrhea without a significant relationship with body mass index. ⁴⁷ Nutritional deficiency is considered one of the important factors that induce dysfunction in the hypothalamic‐pituitary‐ovarian axis. The epidemiological study showed that circulating level of gonadal steroids is suppressed in bushwomen except when food is plentiful and hunting activities restricted. ⁴⁸ It is frequently suggested that vegetarianism is associated with menstrual disturbances. ⁴⁹ , ⁵⁰ , ⁵¹ , ⁵² To predict dysfunction in the hypothalamic‐pituitary‐ovarian axis, irregular menstruation is one of the positive clinical symptoms. A vegetarian low caloric diet may rapidly induce menstrual cycle disorders and a short luteal phase. ⁵³ In women, diets high in fiber, low in fat, or both, concentrations of ovarian hormones or their metabolites may be lower at various points in the menstrual cycle. ⁵⁴ , ⁵⁵ , ⁵⁶ , ⁵⁷ , ⁵⁸ , ⁵⁹ , ⁶⁰ Low weight and fat mass, low calorie intake and eating disorders are speculated to cause disturbance in the pulsatile secretion of pituitary gonadotropins. Similarly, a positive relationship between monounsaturated fat intakes and serum estrogen concentration, and an inverse relationship between fiber and serum estrogen were observed in Japanese women. ⁶¹ , ⁶²

Excess intake of food

In general, it is widely accepted that excess weight and obesity induce diabetes mellitus type 2 and cardiovascular diseases. ⁶³ They are also known to be associated with irregular menstrual cycles, reduced fertility and hormone‐sensitive cancers in young women. ¹⁵ , ¹⁷ Obesity is considered to result in abnormality of sex steroid hormone balance and serum sex hormone‐binding globulin level. In young women, the age of obesity onset is significantly correlated with menstrual irregularities and it is more frequent in women who became obese during puberty than in those who were obese during infancy. ⁶⁴ The recent discovery of leptin, which is a novel hormone produced mainly by adipose cells, ⁶⁵ provided a new explanation for the relationship between menstrual irregularities and obesity as this hormone was demonstrated to regulate gonadotropin surge during puberty. ⁶⁶ , ⁶⁷ A low fat diet was shown to decrease symptoms of dysmenorrhea along with increasing serum sex hormone‐binding globulin concentration. ⁶⁸ , ⁶⁹

In Japan, excessive caloric intake observed in young women is frequently a result of an excessive intake of confectionary and sweet drinks containing artificial sweeteners. It should be noted that the safety of these sweeteners on human health has not yet been proven. ⁷⁰ In fact, a well‐known sweetener called saccharin, has been strongly suspected to induce cancer ⁷¹ and is widely used in these foods in Japan over the recent three decades.

Shift of food customs from Japanese to Westernized style food

As described above, the ratios of unsaturated fatty acids are higher in fish than in meats. Because prostaglandins derived from marine polyunsaturated fatty acids are usually less aggressive, intake of these fatty acids are expected to reduce dysmenorrhea. Several studies showed that dietary supplementation of ω‐3 polyunsaturated fatty acids had a beneficial effect on symptoms of dysmenorrhea in young women. ⁷² , ⁷³ A lower consumption of fish, eggs and fruit was reported to be a risk factor for this pathology together with early menarche, and long and heavy menstrual flow. ⁷⁴ These facts suggest that fish intake facilitates reduction of dysmenorrhea.

Recently, it has been reported that meat contains a considerable amount of natural sex steroid hormones such as 17β‐estradiol, ⁷⁵ whereas soybeans have isoflavone that possesses estrogenic and anti‐oxidant actions. ⁷⁶ , ⁷⁷ In general, two classes of phytoestrogens, lignans and isoflavones, are known. Soy isoflavones are expected to prevent postmenopausal osteoporosis. ⁷⁸ Supplementation with lignans was reported to increase the length of the luteal phase and the ratio of progesterone to estradiol during the luteal phase. ⁷⁹ However, Cassidy et al. observed that isoflavones increased the follicular phase without affecting luteal phase length. ⁸⁰ These effects of Japanese foods on female reproductive functions will be clarified in the future.

It was shown that the westernization of dietary habits is strongly correlated with increased mortality from breast and ovarian cancers in Japan. ²⁸ , ⁸¹ Phytoestrogens are also expected to suppress carcinogenesis. ⁷⁷ Supporting this, a diet high in plant foods was reported to be important in reducing the risk of ovarian cancer. ⁸² Several studies have suggested that isoflavones decrease the risk of breast cancer, but this remains controversial. ⁸³ Recent studies showed that catechins, which are abundant in green teas, have cancer preventing effects. ⁸⁴ , ⁸⁵ These polyphenols were also demonstrated to modulate estrogen action through molecular mechanisms at the serum concentration after tea‐drinking. ⁸⁶ , ⁸⁷

Diet skipping

Recently, we found that young women who skip breakfast have a significantly higher degree of dysmenorrhea symptoms than young women who eat breakfast, suggesting a positive correlation between skipping breakfast and menstrual disorders. ⁹ This study also supported the previous report that breakfast‐skipping induced constipation. ²⁵ Pathophysiologically, pelvic pain is conducted through afferent pathways by the hypogastric sympathetic and parasympathetic nerves, and these efferent pathways mediate constipation. Taken together, it can be speculated that the high frequency of dysmenorrhea observed in young women who skip breakfast reflected some dysfunctional conditions in the pelvic cavity, which were promoted by inappropriate dietary habits. ⁹ Additionally, breakfast skipping may induce some degree of nutritional defect in the morning when social activity is relatively high. Although the mechanism is completely unknown, it is possible that some factors that become deficient by breakfast skipping may be involved in the development of dysmenorrhea. ⁹

Supplementation

A recent study suggested that deficiency of vitamin B1 and magnesium may cause dysmenorrhea, suggesting supplementation of these agents can relieve menstrual symptoms. ⁸⁸ Several studies reported that vitamin deficiency or hypoglycemia induced premenstrual syndrome in which patients complain of irritability, constipation and edema several days before the onset of menstruation. ⁸⁹ However, Nagata et al. reported that intake of green and yellow vegetables, which are rich in carotenoids, could accelerate the onset of menopause. ⁹⁰

Currently, attention has been paid on supplementation of micronutrients such as zinc, iron, vitamin A and folic acid, to young women because deficiency of micronutrients has been shown to cause embryo abnormality and poor pregnancy outcome. ⁹¹ Deficiency of folic acid is significantly related with neural tube defects and other congenital anomalies especially when they take valproic acid or carbamazepine for epilepsy treatment. ⁹² National programs for young women and experimental approaches about supplementation of folic acid have been widely performed. ⁹³ , ⁹⁴ , ⁹⁵ , ⁹⁶ As a result of the dramatic changes in food habits among young women, supplementation of micronutrients to young women in Japan should be considered not only from a gynecologic perspective but also from a perinatological perspective.

Toxic agents

It has been proposed that dioxin is a factor promoting endometriosis. ⁹⁷ Recently, the molecular mechanism by which dioxin can exert estrogenic action, inducing development of endometriosis and estrogen‐dependent tumors has been clarified. ⁹⁸ Although the precise mechanism is still unknown, it was reported that mercury‐exposed workers showed significantly higher incidence of dysmenorrhea. ⁹⁹ As considerable accumulation of mercury and dioxin in fishes has been estimated, exposure to these agents in food should be considered when treating young women who are suffering from dysmenorrhea.

Although the estimated amount of daily intake of food additives did not show a significant increase during the 1990s in Japan, ¹⁰⁰ young people have considerable opportunity to consume foods rich in additives, which are usually sold in convenience stores, especially when they live alone. ⁸ In addition to the above environmental toxins, many food additives being used in Japan have been suggested to adversely affect human health. Many investigators reported that nitrous acid sodium can easily be transformed to harmful N‐nitroso compounds under acidic conditions, that is in the stomach, or in combination of anti‐oxident agents. ¹⁰¹ , ¹⁰² , ¹⁰³ , ¹⁰⁴ , ¹⁰⁵ Furthermore, food colorants, erythrosine (Food Red 3), phloxine B (Food Red 104, D and C Red no. 28) and rose bengal B (Food Red 105), which are commonly used for red dyes in Japanese food including confectionary and sweet drinks, have been proposed to have tumorgenic activity. ¹⁰⁶ , ¹⁰⁷ , ¹⁰⁸ , ¹⁰⁹ , ¹¹⁰

Recently, food additive‐additive chemical interactions have been a great concern because these interactions can cause unexpected adverse effects on human health in the body. ¹¹¹ For example, Kitano et al. demonstrated the possibility that decomposition products of potassium sorbate with ascorbic acid, which are widely used in combination as food additives in Japan, caused mutagenic and DNA‐damaging activity. ¹¹² They emphasized that it is necessary to evaluate the safety of chemicals used as food additives not only before their use, but also after their usage has been introduced.

CONCLUSION

CURRENTLY, MANY COUNTRIES including Japan face various problems concerning food conditions and customs that have been considerably influenced by various foreign sources of information and power. Under these circumstances, the dietary habits of young women in Japan have dramatically changed. This alteration may contribute to increasing socioeconomic QOL, but it also can lead to lower QOL as a result of health problems, inducing gynecologic symptoms and disorders in the female reproductive organs, as well as carcinoma in subsequent reproductive and/or postmenopausal ages.

It should be also noted that latent development of organic diseases such as endometriosis, which are accompanied by dysmenorrhea, can occur under the current nutritional situation in young women. Research in the fields of food science and reproductive medicine is encouraged to cooperatively evaluate the present nutritional environment among young people to improve their QOL as well as reproductive function.