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C S Johnston

Publications and source records attributed to C S Johnston.

At least 19 recordsLinked to original sources
PubMed2001

A reconsideration of the origins of the type 2 diabetes epidemic among Native Americans and the implications for intervention policy.

Type 2 diabetes has reached epidemic proportions in many Native American communities in North America. The overwhelming majority of physicians, biomedical researchers, and medical ecologists continue to explain the astoundingly high prevalence rates of diabetes among Native Americans and other high prevalence populations in terms of yet-to-be-identified genetic factors. Recent experimental and epidemiological research, however, has brought to light an etiological alternative to the genetic-predisposition model. This body of research suggests that type 2 diabetes may result initially from fetal malnutrition and, in subsequent generations, be propagated via perturbations in the intrauterine environment. Native American populations at greatest risk for diabetes today are the ones most likely to have endured severe nutritional stress in their recent histories, thus experiencing the conditions that are most conducive to the diabetic developmental sequence. If further substantiated, the implications of the fetal-origin model of diabetes for diabetes intervention programs are profound.

Adult↗
PubMed2001

Plasma-Saturating intakes of vitamin C confer maximal antioxidant protection to plasma.

OBJECTIVE: Supplemental vitamin C has been shown to reduce oxidative damage in vivo, yet the dose-response relationship between vitamin C intake and antioxidant protection is not known. This report examined blood indicators of oxidative stress in subjects consuming graded doses of vitamin C, from 75 to 2,000 mg/day. METHODS: Ten healthy, non-smoking men and women (26.1 +/- 2.1 years) were recruited from a campus population. During the ten-week study, subjects limited fruit and vegetable consumption (< or = 3 servings/day) and consumed a multivitamin and mineral pill daily. Beginning at week 3, subjects ingested either a vitamin C (n = 8) or placebo (n = 2) capsule, which were identical in appearance and taste. The content of the vitamin C capsule increased every two weeks (from 250 mg at weeks 3-4 to 500 mg, 1,000 mg. and 2,000 mg at weeks 5-6. 7-8. 9-10, respectively). Fasting blood samples were collected at two-week intervals and analyzed for vitamin C, total lipid hydroperoxides and Heinz bodies in packed erythrocytes incubated 24 hours at 37 degrees. RESULTS: Plasma vitamin C rose 55% in vitamin C-supplemented subjects by the end of the ten-week treatment (p < 0.05), and measures of oxidative stress decreased 60% to 90% (8.1 +/- 0.6 to 3.5 +/- 0.4 nmol/mL and 69.1 +/- 7.8% to 6.7 +/- 6.0% for total lipid hydroperoxides and Heinz bodies, respectively). Significant decreases in markers of oxidative stress were noted at the 500 mg, 1,000 mg and 2,000 mg dosages versus placebo. Antioxidant protection was similar at the 1,000 mg and 2,000 mg dosage. CONCLUSIONS: These data indicate that the antioxidant protection afforded by short-term vitamin C supplementation is maximal at the 500-1,000 mg dosage range.

Adult↗
PubMed2000

Infant formula ingestion is associated with the development of diabetes in the BB/Wor rat.

The association between early exposure to cow's milk products in infancy and risk for insulin dependent diabetes mellitus (IDDM) is controversial. We examined whether the ingestion of cow's milk-based infant formula altered the expression of the diabetic syndrome in the BB/Wor rat, an animal model of IDDM. Pregnant BB/Wor dams were obtained from the NIH contract colony at the University of Massachusetts and housed under semi-barrier conditions. Rat pups were intubated with 1 to 2 ml of commercially available cow's milk-based infant formula (Enfamil or Nutramigen) or sham intubated (controls) daily from day 12 to day 25 of life. Pups were weaned at day 25 and monitored for glucosuria daily through 120 days of life. All rats including dams consumed a milk-free rat chow and acidified water ad libitum throughout the study. The mean age of disease onset was 4 to 10 days earlier in Nutramigen-fed and Enfamil-fed rats relative to controls (84+/-3, 78+/-2 and 88+/-4 days, respectively); the mean age of disease onset was significantly different between controls and Enfamil-fed animals (p<0.05). At 120 days, 60% (12/20) of control rats developed diabetes versus 100% of animals fed either type of infant formula prior to weaning (15/15:Enfamil-fed; 19/19:Nutramigen-fed) (p<0.05). These data indicate that direct, early ingestion of cow's milk-based formula was related to the expression of diabetes in the BB/Wor rat.

Animals↗
PubMed2000

Low intakes of vegetables and fruits, especially citrus fruits, lead to inadequate vitamin C intakes among adults.

OBJECTIVE: To determine vitamin C intakes among adults and to identify differences in dietary intake associated with vitamin C consumption. DESIGN: This cross-sectional study compared vitamin C intake, nutrient intake, and food group choices of adults with low (<30 mg/d), marginal (30-60 mg/d), and desirable (>60 mg/d) vitamin C intakes. SUBJECTS: Data from 2472 men and 2334 women aged 25-75 y were obtained from the 1994-1996 Continuing Survey of Food Intakes by Individuals (CSFII). RESULTS: Overall, 18% of the sample had low vitamin C intakes, 24% had marginal intakes, and 58% had desirable intakes. In addition to consuming less vitamin C, adults with low vitamin C intakes consumed significantly less (P</=0.001) energy-adjusted (ie nutrient/1000 kcal) folate, fiber, beta-carotene, and vitamin B6, and significantly more (P<0.001) fat. Compared to adults with low intakes, adults with desirable vitamin C intakes consumed significantly more (P</=0.001) high-vitamin C fruit juice and low-vitamin C vegetables, while consuming significantly less (P</=0.009) soft drinks, coffee/tea and alcoholic beverages. On average, adults with desirable vitamin C intakes consumed more than five daily servings of vegetables and fruits, of which more than one was citrus. Adults with low and marginal vitamin C intakes consumed less than one-fifth of a serving of citrus. CONCLUSIONS: A considerable number of adults under-consume vitamin C and total vegetables and fruits. Nutritionists should continue to promote five to nine daily servings of vegetables and fruits, at least one of which should be rich in vitamin C.

Adult↗
PubMed2000

More Americans are eating "5 a day" but intakes of dark green and cruciferous vegetables remain low.

Epidemiological investigations repeatedly show that the regular consumption of dark green and cruciferous vegetables, tomatoes and citrus fruits in particular is related to reduced cancer risk. We used the 1994-1996 Continuing Survey of Food Intakes by Individuals to examine the types of fruits and vegetables consumed by Americans. The analytic sample population, which consisted of 4806 men and women (25-75 y old) who completed two nonconsecutive 24-h recalls, consumed 3.6 +/- 2.3 servings of vegetables and 1.6 +/- 2.0 servings of fruit daily. Iceberg lettuce, tomatoes, French fried potatoes, bananas and orange juice were the most commonly consumed fruits and vegetables, accounting for nearly 30% of all fruits and vegetables consumed. The most popular items, lettuce and tomatoes, were consumed by 39-42% of the sample population during the reporting period. Fewer respondents (16-24%) consumed French fried potatoes, bananas or orange juice. Only 3% of the sample consumed broccoli during the reporting period. White potato consumption averaged 1.1 servings daily, with French fried potatoes representing 0.4 serving. Tomato product consumption averaged 0.5 serving daily, dark green vegetable consumption averaged 0.2 serving daily and citrus, berries or melon consumption amounted to nearly 0.8 serving daily. These data indicate that Americans are consuming more fruits and vegetables but that dark green and cruciferous vegetable intake is low.

Adult↗
PubMed2000

Nutritional origins of insulin resistance: a rat model for diabetes-prone human populations.

While there has been little success identifying the genetic bases of noninsulin-dependent (type-2) diabetes, current epidemiological data and animal models implicate fetal undernutrition in the development of type-2 diabetes. We examined the effects of fetal undernutrition on insulin responses and glucose tolerance in adulthood in genetically normal rats. Control rats were adequately nourished in utero and consumed nutritionally adequate (N) diets throughout life. Experimental rats (F1 generation) were undernourished in utero and consumed either N or high-energy, high-fat (HF) diets postweaning. The offspring of the experimental rats (F2 generation) received the respective diets of their parent. Body weights of experimental F1 rats at d 4 were 40% less than that of control pups, and they remained significantly smaller than controls throughout adulthood. The experimental F1 rats consuming N diets postweaning had a reduced insulin response (-30%) at 30-min postglucose challenge in adulthood (P > 0.05). However, their offspring (F2 generation) displayed a markedly elevated insulin response [+80% at 30 min (P < 0.05) and + 230% at 120 min (P < 0.001) postglucose challenge]. The insulin response of the F2 generation rats fed the high-energy, HF diet was even more pronounced [+130% at 30 min (P < 0.003) and + 250% at 120 min (P < 0.001) postglucose challenge]. Thus, undernourishment in utero produces striking insulin resistance in genetically normal, well-nourished second-generation rats.

Aging↗
PubMed1999

Substrate utilization and work efficiency during submaximal exercise in vitamin C depleted-repleted adults.

A placebo-controlled, depletion-repletion protocol was utilized to examine the effect of vitamin C status on substrate utilization during a 90 min walk at 50% maximal oxygen consumption (VO2max). Nine vitamin C depleted subjects (plasma vitamin C < 28 mumol/L) agreed to participate in the 5-week study (aged, 27.6 +/- 2.5 years, mean +/- SE; 5 females, 4 males). Subjects were apparently healthy but unaware of their vitamin C status. Prior to the experimental period, VO2max was measured using open-circuit spirometry during a graded walking protocol. Subjects ingested a placebo capsule daily during weeks 1-3 and a 500 mg vitamin C capsule daily during weeks 4-5 of the experimental study. Mean plasma vitamin C rose nearly 3-fold and mean plasma carnitine fell by nearly 20% at repletion (week 5) versus depletion (week 3). At the end of weeks 3 and 5, subjects completed a 90 minute treadmill walk at an exercise intensity of 50% VO2max. The relative contribution of fat utilized for energy during walking did not differ in the vitamin C depleted versus repleted states. However, work performed by subjects and gross efficiency during exercise increased significantly at repletion versus depletion (10% and 15%, respectively). These data indicate that vitamin C depletion is associated with reduced work efficiency during submaximal exercise.

Adult↗
PubMed1999

Intakes of vitamin C, vegetables and fruits: which schoolchildren are at risk?

OBJECTIVE: The purpose of this study was to determine vitamin C intakes among American schoolchildren. We investigated the leading sources of vitamin C in children's diets, the leading vegetables and fruits consumed by children and differences in dietary intake associated with vitamin C consumption. METHODS: Data from 1,350 7- to 12-year-old and 908 13- to 18-year-old schoolchildren were obtained from the 1994-1996 Continuing Survey of Food Intakes by Individuals (CSFII). The children were stratified by age and gender and then split into three vitamin C consumption groups based upon two 24-hour recalls: low (0 to 30.0 mg), marginal (30.1 to 59.9 mg), and desirable (>60.0 mg). Data were analyzed by tabulation and by ANOVA followed by post hoc Scheffe's test. Outcome measures included food groups and energy-adjusted intakes of micro- and macronutrients. RESULTS: Among the 7- to 12-year-olds, 12% of boys and 13% of girls had mean vitamin C intakes that were less than 30 mg/day, and, among 13- to 18-year-olds, 14% of boys and 20% of girls had low vitamin C intakes. In addition to consuming significantly more vitamin C, children with desirable vitamin C intakes also consumed significantly more (p <0.001) energy-adjusted folate and vitamin B6; children with low vitamin C intakes tended to have significantly greater (p <0.001) energy-adjusted intakes of fat and saturated fat. Children with desirable vitamin C intakes consumed significantly more (p <0.006) high-vitamin C fruit juice, low-vitamin C vegetables and whole milk. Children with low vitamin C intakes on average consumed two daily servings of vegetables and fruits, of which less than 1/5 of a serving was citrus, while children with desirable vitamin C intakes consumed an average of one daily serving of citrus. CONCLUSIONS: A considerable number of children drastically under-consumed vitamin C and total vegetables and fruits. Overall, children with desirable vitamin C intakes had healthier diets, including more milk and vegetables, than did their peers with low vitamin C intakes. Health care professionals should continue to promote at least five daily servings of vegetables and fruits and should advise parents that at least one of these should be rich in vitamin C.

Adolescent↗
PubMed1999

Biomarkers for establishing a tolerable upper intake level for vitamin C.

Dietary reference intakes (DRIs) for vitamin C for healthy U.S. populations are currently being formulated by the Panel on Dietary Antioxidants and Related Compounds of the Food and Nutrition Board of the Institute of Medicine. A major task of the Panel is to analyze the evidence of adverse effects of high-dose vitamin C intakes to derive, if appropriate, a Tolerable Upper Intake Level (UL) for vitamin C. The present report details current and past research examining potential adverse effects of supplemental vitamin C. The available data indicate that very high intakes of vitamin C (2-4 g/day) are well tolerated biologically in healthy mammalian systems. Currently, strong scientific evidence to define and defend a UL for vitamin C is not available.

Adult↗
PubMed1998

Vitamin C status of an outpatient population.

OBJECTIVE: To determined the prevalence of vitamin C deficiency (plasma vitamin C concentrations less than 11.4 mumol/L) and vitamin C depletion (plasma vitamin C concentrations from 11.4 to less than 28.4 mumol/L) in an outpatient population. SUBJECTS AND METHODS: A consecutive sample of patients presenting at a health maintenance organization laboratory for outpatient procedures was utilized. Plasma vitamin C concentrations were determined in 350 females and 144 males, aged 6 to 92 years (mean +/- SD: 46.7 +/- 18.7 years). RESULTS: The mean plasma vitamin C concentration for all subjects was 32.4 +/- 13.6 mumol/L. Mean plasma vitamin C did not vary by sex, race, or fasted state. Diabetics had a significantly lower mean plasma vitamin C concentration (25.6 +/- 10.8 mumol/L) compared to patients presenting for general check-up/gynecological exams (33.5 +/- 14.8 mumol/L) or pregnancy exams (32.4 +/- 9.7 mumol/L). Six percent of subjects had plasma vitamin C concentrations indicative of vitamin C deficiency (n = 31), and 30.4% of the sample were vitamin C depleted (n = 150). The prevalence of vitamin C deficiency or vitamin C depletion did not differ by race or visit category. CONCLUSIONS: Surprisingly high rates of vitamin C deficiency and vitamin C depletion were evident among generally healthy, middle class patients visiting a health care facility for routine health exams, gynecological exams, and pregnancy exams.

Adolescent↗
PubMed1998

Vitamin C status of a campus population: college students get a C minus.

Diet and the vitamin C status of two samples of college students were examined. Nonsmoking participants were recruited from a campus population during the fall and winter months. The prevalence of vitamin C deficiency (plasma vitamin C concentrations less than 11 mumol/L) ranged from 1% to 2% in the sampled campus populations. Marginal vitamin C status (plasma vitamin C concentrations from 11 to less than 28 mumol/L) was observed in 12% of the fall sample and 16% in the winter sample. Participants with marginal vitamin C status consumed significantly fewer servings of fruits and vegetables daily than participants with adequate vitamin C status. Marginal vitamin C status, which is even more pronounced in smokers, has been associated with fatigue and increased severity of respiratory tract infections. Because the vitamin C status of many college students, both smokers and nonsmokers, may be inadequate, health promotion or wellness programs for all students should emphasize the importance of adequate fruit and vegetable consumption.

Adult↗