Evolution of Evidence for Selected Nutrient and Disease Relationships (2002) / Chapter Skim
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2 Case Studies
2 Case Studies
Pages 19-50
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From page 19... ...
(NRC, 1989) and the Dietary Reference Intake (DRI)
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From page 20... ...
The incidence of dental caries was 50 to 60 percent lower after water was fluoridated than before, but increased to prefluoridation levels when fluoridation was discontinued.
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640~. Dietary Reference Intake Report The DRI report, Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride (IOM, 1997)
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Additional studies conducted after the D&H report and considered in the DRI report provided evidence that fluoridated water, dietary supplements, and topical application of fluoride reduce dental caries at all ages. Calcium and Bone Status This section discusses dietary calcium in relation to bone status and osteoporosis and in relation to fracture risk.
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From page 23... ...
The findings did not consistently support a relationship between calcium intake and bone mass or rate of bone loss if measured in women after menopause. In observational studies reporting that people with diagnosed osteoporosis consumed less calcium than age-matched controls, the intakes were usually less than 800 mg of calcium/day.
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From page 24... ...
Dietary Reference Intake Report Osteoporosis. Calcium was discussed in the report, Dietary Reference Intakes for Calcium, Phosphorous, Magnesium, Vitamin D, and Fluoride (IOM, 1997~.
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Bone Fracture. With respect to bone fracture as the major outcome, several calcium intervention studies conducted during the 1990s in both institutionalized and noninstitutionalized persons revealed a linkage between calcium intake, reduced bone resumption, and a reduction in bone fractures.
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From page 26... ...
Although the DRI report is cautious in its interpretation, data from clinical trials designed to study the effect of varying calcium intakes on bone mass were used along with data on calcium retention to establish the AI of calcium for adult populations. It is unlikely that evidence from epidemiological, ecological, or clinical trials will ever define a direct causal link between dietary calcium intake in early life and osteoporosis risk later in life.
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From page 27... ...
Dietary Reference Intake Report The observations of the prevalence of vitamin D deficiency in postmenopausal women and the elderly and the association with osteoporosis noted in the D&H report were further substantiated by studies conducted in the 1990s (Chapuy et al., 1992; Honkanen et al., 1990; McKenna, 1992; Pietschmann et al., 1990) and reported in Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride (IOM, 1997~.
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From page 28... ...
The D&H report cited 12 epidemiological studies, including both case-control and cohort studies, that found inverse associations between either dietary intake of Q-carotene or plasma or serum levels of Q-carotene and risk of lung cancer. While it was recognized that the estimates of intake were derived from measures of fruit and vegetable consumption, there were supportive data from animal studies indicating that p-carotene as a single
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From page 29... ...
Dietary Reference Intake Report In the years between publication of the D&H report and the DRI report Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (IOM, 2000a) , considerable research evolution occurred.
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In this case, it appeared that cigarette smokers and asbestos-exposed individuals were harmed, but former smokers had no increase in risk of lung cancer with supplementation. These advances in understanding were the result of time and a substantial financial investment in randomized clinical trials.
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488~. Dietary Reference Intake Report The DRI text on vitamin C and gastric cancer was limited in that the emphasis of this report, Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (IOM, 2000a)
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The epidemiological studies mentioned in the D&H report used plasma or serum vitamin E levels to assess vitamin E status. While there was no consistent observed effect of only vitamin E on cancer risk, it was noted that "low serum levels of vitamin E and selenium may be related to increased risk of some cancers, such as breast and lung cancers" (p.
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The largest was a clinical trial of vitamin E for the primary prevention of lung cancer in heavy smoking men from Finland (ATBC, 1994~. No reduction in lung cancer risk was noted in men randomized to receive supplemental vitamin E
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Dietary Reference Intake Report The DRI report, Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (IOM 2000a) , differs substantially from the D&H report.
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The results of clinical trials that tested the impact of vitamin E supplements on CHD events were also summarized in the DRI report. In 1994, the ATBC trial, which tested the impact of vitamin E on lung cancer in 29,133 Finnish male smokers, documented a nonsignificant impact of this supplement (50 mg/day of all rac-a-tocopherol acetate)
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From page 36... ...
In contrast, the DRI report presents a qualitative overview of available evidence from a variety of categories. While the mechanistic and animal studies strongly support the oxidative modification hypothesis, it is likely that the prospective observational studies, published in the early 1990s, fueled interest in the potential impact of vitamin E supplements on CHD and converted the relationship from uncertain to promising.
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515~. Dietary Reference Intake Report The relationship of vitamin C to colds was also not a major focus in the DRI report, Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (IOM, 2000a)
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From page 38... ...
Thus, the report did not discuss whether vitamin C may reduce the duration of colds. Folate and Cervical Dysplasia Diet and Health Report The D&H report cited data from one randomized, controlled intervention study, which suggested a possible benefit of supplemental folate on the progression of cervical dysplasia.
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From page 39... ...
Since cervical infection with HPV-16 significantly increases the risk for cervical cancer, this study provides evidence that suboptimal body reserves of folate, as reflected in low red blood cell levels, influence a key risk factor associated with early cervical cancer. The mechanistic animal studies also cited in the DRI report provided supporting evidence for the role of impaired folate status on carcinogenesis.
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Studies cited in the DRI report do support the hypothesis that less than adequate folate status may increase the risk for cervical dysplasia when coexisting risk factors are present. However, data do not support an inverse relationship between cervical cancer and folate supplementation.
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In addition, research evidence suggests that once the cervical dysplasia has advanced to the neoplastic stage, the inverse association between folate status and disease risk is no longer detectable. Phosphorus and Bone Status Diet and Health Report The review of phosphorus in the D&H report centered on the importance of the ratio of dietary calcium to phosphorus (Ca:P ratio)
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No information on a possible relationship between phosphorus intake and bone mass was included. Evolution Uncertain to Uncertain The shift in perspective about the importance of the ratio of dietary calcium to phosphorus may be credited to the many balance studies in humans that did not demonstrate abnormalities in calcium homeostasis imposed by high dietary phosphorus.
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630~. Dietary Reference Intake Report The DRI report, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (IOM, 2001)
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From page 44... ...
Dietary Reference Intake Report The DRI report, Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6' Folate, Vitamin By, Pantothenic Acid, Biotin) and Choline (IOM, 1998)
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From page 45... ...
The results of the controlled intervention trials reported in 1991 and 1992 were supported by the collective findings of observational studies published primarily between 1988 and 1995. None of the observational studies could identify folate specifically as the vitamin responsible for reducing NTDs.
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Dietary Reference Intake Report The DRI report, Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin By, Pantothenic Acid, Biotin, and Choline (IOM, 1998) , stated, "experimental data indicate that changes in folate status may influence the process of neoplastic changes in certain epithelial tissue: a negative change in folate status may stimulate carcinogenesis.
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Data have evolved that strengthen the inverse association between folate status and colorectal cancer. Definitive conclusions related to the impact of folio acid supplementation on colorectal neoplasia await the results of ongoing controlled intervention trials.
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More definitive evidence for a causal relationship between folate status and colorectal cancer may be provided by the ongoing prospective, controlled intervention trials. Vitamin E and Prostate Cancer Diet and Health Report report.
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Thus, the relationship between supplemental vitamin E and prostate cancer prevention is perhaps best characterized as promising.
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