Dietary factors

Three hormones regulate turnover of calcium in the body (22). 1,25-Dihydroxycholecalciferol is a steroid derivative made by the combined action of the skin, Hver, and kidneys, or furnished by dietary factors with vitamin D activity. The apparent action of this compound is to promote the transcription of genes for proteins that faciUtate transport of calcium and phosphate ions through the plasma membrane. Parathormone (PTH) is a polypeptide hormone secreted by the parathyroid gland, in response to a fall in extracellular Ca(Il). It acts on bones and kidneys in concert with 1,25-dihydroxycholecalciferol to stimulate resorption of bone and reabsorption of calcium from the glomerular filtrate. Calcitonin, the third hormone, is a polypeptide secreted by the thyroid gland in response to a rise in blood Ca(Il) concentration. Its production leads to an increase in bone deposition, increased loss of calcium and phosphate in the urine, and inhibition of the synthesis of 1,25-dihydroxycholecalciferol. 

Breast Cancer. Many studies have observed low incidences of hormone-dependent cancers, particularly breast cancer, in Asian countries compared with Western countries and it is becoming increasingly accepted that dietary factors play an important role. Although breast cancer can occur in either males or females, only about 1 % of all cases occur in men, and male breast cancer is a rare disease in all parts of the world." Although there appear to be some similar risk factors for breast cancer in males and females, there is no indication in the literature that diet is either a risk or a protective factor for male breast cancer. The development of breast cancer is known to be highly dependent on the hormones associated with female reproductive functions, while established genetic factors have been... 

Several studies have investigated the role of dietary factors in prostate cancer risk, but results appear inconsistent. Significant effects have not been detected for dietary soya products certain vegetables, beans, fruit, rice and seaweed appear to be protective in some studies, while another has shown no protective effect from seaweed or vegetable consumption. In addition, a number of other risk factors have been shown to be associated with an increased risk of this cancer, including meat and dairy products and carotenoids. 

As long ago as the 1930s Rusznyak and Szent-Gyorgi proposed that the flavonoids were an essential dietary factor contributing to the maintenance... 

Mortality rates from CVD are generally lower in Asian populations compared to Western populations (Knight and Eden, 1996). Although many dietary factors are known to play a protective role in CVD and it has been suggested that phytoestrogen content of Asian diets may be responsible for the cardioprotective effect. 

The pattern of hormonal risk factors involved in the development of endometrial cancer is similar to those associated with the development of breast cancer. In addition, there is substantial evidence to suggest that HRT can increase the risk (Beral et al, 1999 Bingham et al, 1998). Compared to the UK, the incidence of endometrial cancer in countries such as Japan is relatively low (Bingham et al, 1998). It has been suggested that dietary factors may be responsible for the reduced incidence, and there is indirect evidence from epidemiology studies which suggests that increased consumption of soy products may lower the risk of endometrial cancer. However, these data are not conclusive. To date, no studies have demonstrated a link between consumption of phytoestrogens and an increased risk of endometrial cancer. 

Substantial individual differences were observed in the response to study breads and the ranges of enterolactone concentration changes in the groups were as follows -54.5-60.0 nmol/1 (placebo), -26.2-101.3 nmol/1 (LP), -19.6-81.8 nmol/1 (HP). This was something that could have been expected as in several studies dietary factors have explained only 10% of the variation in serum enterolactone (Vanharanta et al, 2002b Kilkkinen et al., 2001). This gives further support to the major role of intestinal bacteria in the synthesis of enterolactone. Decreased concentrations of enterolactone may occur due to an increased fiber intake, which may shorten the retention time in the colon and lead to incomplete metabolism of plant lignans. Constipation was earlier shown to be associated with an increased level of serum enterolactone (Kilkkinen et al., 2001). 

Burnstein, M.J. (1992). Dietary factors related to colorectal neoplasms. Sutg. Clin. North Am. 73, 13-29. 

Dietary factors such as coffee, tea, cola, beer, and a highly-spiced diet may cause dyspepsia, but they have not been shown to independently increase PUD risk. Although caffeine increases gastric acid secretion and alcohol ingestion causes acute gastritis, there is inconclusive evidence to confirm that either of these substances are independent risk factors for peptic ulcers. 

Colon cancer occurs at a much higher rate in industrialized parts of the world such as North America and Europe, whereas the lowest rates are seen in less-developed areas, suggesting that environmental and dietary factors influence the development of colon cancer.2 In addition to these environmental factors, colon cancers are known to develop more frequently in certain families, and genetic predisposition to this cancer is well known. 

In summary, the true association between most dietary factors and the risk of colon cancer is unclear. The protective effects of fiber, calcium, and a diet low in fat are not completely known. Lifestyle factors such as NSAID use and hormone use appear to decrease the risk of colorectal cancer, whereas physical inactivity, alcohol use, and smoking appear to increase the risk of colon cancer. Clinical risk factors and genetic mutations are well-known risks for colon cancer. 

Other dietary factors implicated in prostate cancer include retinol, carotenoids, lycopene, and vitamin D consumption.5,6 Retinol, or vitamin A, intake, especially in men older than age 70, is correlated with an increased risk of prostate cancer, whereas intake of its precursor, [3-carotene, has a protective or neutral effect. Lycopene, obtained primarily from tomatoes, decreases the risk of prostate cancer in small cohort studies. The antioxidant vitamin E also may decrease the risk of prostate cancer. Men who developed prostate cancer in one cohort study had lower levels of l,25(OH)2-vitamin D than matched controls, although a prospective study did not support this.2 Clearly, dietary risk factors require further evaluation, but because fat and vitamins are modifiable risk factors, dietary intervention may be promising in prostate cancer prevention. 

Other dietary factors that may influence overall caffeine consumption include foods that contain cocoa or chocolate, such as candies and sweets. These products do not contribute as much caffeine as either coffee or tea however, their contribution to caffeine exposure should be recognized. Caffeine may also be in foods and beverages as an additive, which the Food and Drug Administration monitors and requires to be labeled on the product. 

A number of dietary and nondietary variables have been proposed as risk factors for osteoporosis. Among dietary factors, the relation between caffeine intake and bone health has been studied extensively. Although proof that caffeine adversely affects calcium metabolism and is detrimen-... 

Kreiger, N., Gross, A., Hunter, G., Dietary factors and fracture in postmenopausal women a case-control study, International Journal of Epidemiology, 21, 953, 1992. 

Garber BT, Wei E. 1974. Influence of dietary factors on the gastrointestinal absorption of lead. 

Differences in environmental and dietary factors may contribute to the differences in allele frequencies in the African/African American, Caucasian and Asian populations. PGP exists in several normal tissues where it probably has the physiological role of excreting xenobiotics and protecting important tissues from such compounds when they are present in the blood [62, 63]. Allelic differences of sev-... 

Canh T T, Aamink A J A, Verstegen M W A and Schrama J W (1998), Influence of dietary factors on the pH and ammonia emission of slurry from growing-finishing pigs , J Anim Sci, 76, 1123-1130. 

Farchi S, Forastieri F, Agabiti N, Corbo G, Pistelli R, Fortes C, DelPOrco V and Perucci C. 2003. Dietary factors associated with wheezing and allergic rhinitis in children. Eur Respir J 22 772—780. 

Goodman MT, Kolonel TJ, Wilkens, LR, Yoshizawa CN, Le Marchand L and Hankin JH. 1992. Dietary factors in lung cancer prognosis. Eur J Cancer 28 495-501. 

Howe G, Hirohata T, Hislop T, Iscovich J, Yuan J, Katsouyanni K, Lubin F, Marubini E, Modan B, Rohan T, Toniolo P and Shunzhang Y. 1992. Dietary factors and risk of breast cancer combined analysis of 12 case-control studies. J Nat Cancer Inst 82 561-569. 

The enzyme mediating remethylation, 5-methyltetrahy-drofolate-betaine methyltransferase (Fig. 40-4 reaction 4), utilizes methylcobalamin as a cofactor. The kinetics of the reaction favor remethylation. Faulty remethylation can occur secondary to (1) dietary factors, e.g. vitamin B12 deficiency (2) a congenital absence of the apoenzyme (3) a congenital inability to convert folate or B12 to the methylated, metabolically active form (see below) or (4) the presence of a metabolic inhibitor, e.g. an antifolate agent that is used in an antineoplastic regimen. 

This chapter reviewed current research pertaining to selected environmental agents and autoimmune diseases (Table 25.3). Other infectious agents (e.g., parvovirus, varicella), occupational exposures (e.g., mercury), dietary factors (dietary supplements, nutrients such as antioxidants, and specific proteins in wheat and other grains implicated in celiac disease), and stress have been the focus of additional research that was not included in this review. 

The importance of dietary or endogenously synthesized vitamin D has long been recognized as a primary factor influencing the bioavailability of calcium. Some of the most exciting biochemical-nutritional research in recent years has been devoted to determining the mechanisms involved in vitamin D-calcium interactions. This research has been well reviewed in other publications. The objective of the symposium upon which this book is based was to review some of the other lesser-known dietary factors that appear to have an impact on the bioavailability of calcium. 

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