Ethnic differences in osteocalcin gamma-carboxylation, plasma phylloquinone (vitamin K1) and apolipoprotein E genotype.

OBJECTIVE: To investigate plasma osteocalcin gamma-carboxylation and its relationship to plasma phylloquinone concentration and apolipoprotein E (apoE) genotype in women from three ethnic groups with differing osteoporotic fracture risk. DESIGN AND SUBJECTS: Fasted blood samples were collected from postmenopausal Gambian (n=50), British (n=31) and Chinese women (n=23), and 11 premenopausal women in each group from three cross-sectional studies. RESULTS: After adjustment for total osteocalcin, plasma undercarboxylated osteocalcin (adjusted ucOC) was lowest in Chinese and highest in British women postmenopause (British vs Chinese 103% higher, P<0.0001; Gambian vs Chinese 66% higher, P<0.01). No differences were observed premenopause. Within each ethnic group, adjusted ucOC was similar pre- and postmenopause. Postmenopause, plasma phylloquinone was higher in Chinese women (1.0 ng/ml) than in British (0.31 ng/ml) and Gambian women (0.36 ng/ml) (P<0.0001). Premenopause, plasma phylloquinone was higher in Gambian and Chinese women (0.6 ng/ml) than in British women (0.3 ng/ml; P=0.01). Plasma phylloquinone and adjusted ucOC were inversely related in postmenopausal British women (R2=32.4%; P=0.0008). ApoE4 frequency was Gambian 32.6%, British 13.8% and Chinese 6%. A lower adjusted ucOC was associated with apoE2 genotype in British and Chinese women. Ethnic differences in adjusted ucOC persisted after adjustment for phylloquinone and apoE genotype. CONCLUSION: These preliminary data indicate suboptimal vitamin K status in postmenopausal British compared to Chinese and Gambian women. Ethnic differences in apoE genotype may also influence osteocalcin gamma-carboxylation status. The study highlights the need for larger epidemiological investigations of ethnic differences in vitamin K status and the possible implications to bone health.

Effect of calcium supplementation on bone mineral accretion in gambian children accustomed to a low-calcium diet.

BACKGROUND: Rural Gambian children have poor growth, delayed puberty, a low bone mineral content, and a low calcium intake. OBJECTIVE: We investigated the effect of a calcium supplement on bone mineral accretion in rural Gambian children. DESIGN: A randomized, double-blind, placebo-controlled study was conducted in 160 children (80 boys, 80 girls) aged 8.3-11.9 y. Bone mineral content (BMC), bone mineral density (BMD), and BMC adjusted for bone width, body weight, and height (size-adjusted BMC) were measured at the midshaft and distal radius. Each child received either 1000 mg Ca/d (as calcium carbonate) or a placebo 5 d/wk for 12 mo. Supplementation increased calcium intake from 342 to 1056 mg/d (8.6 to 26.4 mmol/d). RESULTS: Calcium supplementation resulted in a higher BMC, BMD, and size-adjusted BMC (&xmacr; difference +/- SE): midshaft radius-BMC (3.0 +/- 1.4%; P = 0.034), BMD (4.5 +/- 0.9%; P

An investigation of ethnic differences in bone mineral, hip axis length, calcium metabolism and bone turnover between West African and Caucasian adults living in the United Kingdom.

The aim of the study was to investigate factors relating to calcium and bone metabolism which might explain the low incidence of osteoporotic fracture among Africans. Adult bone mineral status, hip axis length and biochemical indices were investigated in 20 Caucasians (10 male, 10 female) and 19 Gambians (12 male, 7 female) living in the UK. Bone mineral content (BMC), bone mineral density (BMD) and BMC adjusted for bone area, body weight and height (size-adjusted BMC) were measured for the whole-body, lumbar spine, femoral neck, trochanter, radius shaft and radius wrist using dual-energy X-ray absorptiometry. There were no significant differences in whole body or regional BMC; values tended to be lower in the Gambians. Gambian men had higher size-adjusted BMC at the femoral neck (Gambian-British = 21%, 95% CI = 6 to 36%, p < 0.01), associated with a smaller bone area (Gambian-British = -11%, 95% CI = -20 to -2%, p = 0.02). BMD was affected similarly. No other significant differences in BMD or size-adjusted BMC were observed. Gambians had shorter hip axis length (Gambian British, after accounting for sex, = -5%, 95% CI = -9 to -1%, p = 0.02). There were no significant differences in bone turnover (osteocalcin, bone isoenzyme of alkaline phosphatase, urinary deoxypyridinoline) or calciotropic hormone levels (parathyroid hormone, 1,25-dihydroxyvitamin D, calcitonin). Gambian men had lower 25-hydroxyvitamin D concentrations (Gambian = 26.3 SD 12.0 nmol/L, British = 55.5 SD 13.9 nmol/L, p < 0.0001), a difference not seen among the women. Gambian men and women excreted significantly less phosphate and potassium than British subjects by 30-60%; urinary calcium and sodium excretion were similar in the two groups. This study revealed few ethnic differences that could account for the disparity in osteoporotic fracture rates between Africans and Caucasians, with the possible exception of anatomical differences in the hip.

An evaluation of the informed consent procedure used during a trial of a Haemophilus influenzae type B conjugate vaccine undertaken in The Gambia, West Africa.

It has recently been debated whether it is possible or desirable to have one internationally recognised standard of "informed consent" or whether research ethics should be adapted to the culture and educational level of the study population. This study examined the attitudes of the Gambian people to consent to medical research, and evaluated the informed consent process used in a major efficacy trial of a Haemophilus influenzae vaccine. Consent was requested after parents had received a verbal explanation and an information sheet which described the vaccine trial in a local language. A semi-structured interview was conducted with 137 acceptors and 52 refusers. Certain points of knowledge were recalled well by the acceptors; 90% knew the purpose of the vaccine was to prevent disease, but the placebo control design was understood by only 10%. The prime motive for consenting was to receive the HIB vaccine (93%) and that for refusing was that the vaccine was experimental (35%) and might have unknown side effects (29%). Although parents took advice from researchers (50%), health workers (24%), friends (16%) and family (12%), in all cases the decision was made by one of the child's parents. Only 1% of parents sought the opinion of traditional or religious leaders. The principles of informed consent, that it should be free, autonomous and informed were affirmed by this community. Therefore, in The Gambia, the international code of informed consent is appropriate.

Bone changes after 3 mo of lactation: influence of calcium intake, breast-milk output, and vitamin D-receptor genotype.

Factors influencing the change in bone mineral after 3 mo of lactation were investigated in 47 breast-feeding mothers, 11 formula-feeding mothers, and 22 nonpregnant, nonlactating control subjects. At 6-8 wk postpartum, the breast-feeding group had a mean (+/-SD) calcium intake of 34.8+/-13.2 mmol/d and breast-milk volume, calcium concentration, and calcium output of 0.865+/-0.230 L/d, 7.41+/-1.25 mmol/L, and 6.41+/-2.00 mmol/d, respectively. There was no relation between calcium intake and any breast-milk variable. Dual-energy X-ray absorptiometry of the whole body, spine, hip, and forearm was performed at 0.5 and 3 mo. There were significant decreases in bone mineral content at the spine (3.96%; 95% CI: 4.86%, 3.06%), femoral neck (2.39%; 95% CI: 3.61%, 1.17%), total hip (1.51%; 95% CI: 2.45%, 0.60%), and whole body (0.86%; 95% CI: 1.29%, 0.43%) in breast-feeding mothers but not in formula-feeding mothers or nonpregnant, nonlactating women. These changes were not related to calcium intake, breast-milk calcium concentration, vitamin D-receptor genotype, postpartum weight change, or use of the progesterone-only contraceptive pill. After adjustment for bone area, breast-milk volume and height were identified as significant predictors at the spine, such that greater decreases were associated with taller mothers (P = 0.007) and those with greater breast-milk volume (P = 0.001). This finding suggests that the marked bone mineral changes observed in breast-feeding mothers represented a physiologic response to lactation that was independent of dietary calcium supply.

Vitamin D status does not influence the breast-milk calcium concentration of lactating mothers accustomed to a low calcium intake.

Plasma 25-hydroxy-vitamin D and breast-milk calcium concentration were measured at 3 months of lactation in 60 Gambian mothers accustomed to a low calcium diet, of whom 30 were consuming a calcium supplement and 30 were receiving a placebo, and in 48 British mothers. The plasma 25-hydroxy-vitamin D concentration of the Gambian women was not affected by either calcium supplementation (supplemented, 64.4 +/- 2.5 nmol l(-1); placebo, 64.9 +/- 3.5 nmol l(-1); mean +/- SE) or season. The British average was lower (53.9 +/- 3.0 nmol l(-1), p = 0.004), owing to marked seasonal effects. The breast-milk calcium concentration was lower in The Gambia (supplemented, 5.38 +/- 0.13 mmol l(-1); placebo, 5.10 +/- 0.13 mmol l(-1); British, 6.93 +/- 0.15 mmol l(-1), p < 0.0001). There was no relationship between plasma 25-hydroxy-vitamin D and breast-milk calcium concentration in any group. There was no trend towards lower breast-milk calcium concentration in women with vitamin D status towards the bottom of the normal range or in British women during the winter. This study provides no support for the hypothesis that breast-milk calcium concentration is influenced by vitamin D status or that lactating women with a low calcium intake are at particular risk of vitamin D deficiency.

The effect of long-term calcium supplementation on indices of iron, zinc and magnesium status in lactating Gambian women.

The effect of long-term supplementation with CaCO3 on indices of Fe, Zn and Mg status was investigated in a randomized, double-blind intervention study of sixty lactating Gambian women. The supplement contained 1000 mg Ca and was consumed between meals 5 d/week, for 1 year starting 1.5 weeks postpartum. Compliance was 100%. Plasma ferritin concentration, plasma Zn concentration and urinary Mg output were measured before, during and after supplementation at 1.5, 13, 52 and 78 weeks postpartum. No significant differences in mineral status were observed at any time between women in the supplement and placebo groups. Analysis of the longitudinal data series showed that plasma ferritin and Mg excretion were characteristic of the individual (P < 0.001). Within individuals, ferritin concentration was higher at 1.5 weeks postpartum than later in lactation (P = 0.002). Plasma Zn concentration was lower at 1.5 weeks postpartum than at other times (P < 0.001), an effect which disappeared after albumin correction. Low plasma concentrations of ferritin and Zn indicated that the Gambian women were at high risk of Fe and Zn deficiency. Measurements of alpha 1-antichymotrypsin suggested that the results were not confounded by acute-phase responses. The results of the present study indicate that 1000 mg Ca as CaCO3 given between meals does not deleteriously affect plasma ferritin and Zn concentrations or urinary Mg excretion in women who are at risk of Fe and Zn deficiency.

PIP: During March 1990-March 1991, 60 lactating mothers were recruited into a randomized, placebo-controlled trial designed to examine the effect of calcium (Ca) supplementation on plasma zinc (Zn) and ferritin (Fe) concentrations and on magnesium (Mg) excretion during and after Ca supplementation. The women lived in Keneba and Manduar villages in rural Gambia. They consumed 1000 mg Ca or the placebo (2 tablets of dextrose) between meals 5 days/week for 12 months beginning 1-5 weeks postpartum. All women complied. At no time were there significant differences in the indices used to determine Zn, Fe, and Mg status between lactating women on Ca supplements and those receiving the placebo. In fact, the mean differences were less than 10% of the total value. Many women (33-50%), regardless of supplementation group, had a plasma Fe concentration lower than 12 mcg/l, indicating depleted Fe stores. Many women also had low plasma Zn levels. Within individuals, plasma Zn concentrations were 15% lower at day 9 than later in lactation (p 0.001), while plasma Fe levels were 10% higher (p = 0.002). Plasma Zn levels were associated with plasma albumin levels (p 0.001). When adjusted for albumin, the effect of lactation on Zn disappeared. When compared with British women, Gambian women had a lower plasma Zn concentration (p 0.001). Within individuals and after adjustment for lactation stage and for albumin, plasma Zn levels varied between seasons (i.e., hot season values higher than other seasons) (p = 0.004). Women were more likely to excrete Mg during the hot season (p 0.001). These findings indicate that ingestion of 1000 mg Ca between meals has no adverse effect on plasma Fe and Zn levels or urinary Mg excretion in women at risk of Zn and Fe deficiency.

Measurement of starch digestion of naturally 13C-enriched weaning foods, before and after partial digestion with amylase-rich flour, using a 13C breath test.

Malnutrition in infancy is a global problem which leads to retardation of childhood growth and development. There is a pressing need to improve weaning strategies for infants of the developing world. Traditional Gambian weaning foods are watery and of low energy density, but addition of energy in the form of fat and carbohydrate leads to thick, viscous gruels which are difficult to ingest. Partial digestion with amylase (EC 3.2.1.1)-rich flour reduces their viscosity while retaining their energy density. The aim of the present study was to measure the digestibility of a maize-based weaning food, before and after amylase digestion, in malnourished children using a 13C breath test. Ten children (aged 7-16 months; mean weight-for-age Z score -0.8) received isovolumetric and isoenergetic quantities of a maize-based weaning food naturally abundant with 13C. Breath samples were collected at intervals of 30 min for 5 h thereafter and 13CO2 enrichment was measured by isotope-ratio mass spectrometry. Percentage dose of 13C recovered increased from a mean 13.7 (SD 3.7)% before, to 18.3 (SD 5.6)% after ingestion of amylase-treated weaning foods (P < 0.1). There was a significant inverse relation between age and weight, and percentage dose of 13C recovered in children receiving amylase-treated feeds. There were no differences in concentrations of amylase in saliva of infants or breast milk of their mothers. Partial digestion of supplementary foods may improve the nutrition of undernourished weaning children, not only by reducing their viscosity, thereby increasing ingestion, but also by improving their digestion and thereby their absorption.

Calcium requirements of lactating Gambian mothers: effects of a calcium supplement on breast-milk calcium concentration, maternal bone mineral content, and urinary calcium excretion.

The calcium requirement for prolonged lactation was investigated in a randomized supplementation study of Gambian mothers consuming a low-calcium diet (7.1 mmol/d, or 283 mg/d). Sixty women were studied from 10 d to 78 wk of lactation, receiving calcium or placebo for the first 12 mo. The supplement increased average calcium intake by 17.9 mmol/d (714 mg/d). Supplementation had no effect on breast-milk calcium concentration or on maternal bone mineral content. Urinary calcium output was higher in supplemented than in unsupplemented mothers by 1.18 mmol/d (47 mg/d), P < or = 0.005. Longitudinal changes in urinary calcium output and bone mineral content made a substantial contribution to calcium requirements for lactation. This study suggests that, in women with low calcium intakes, there is no direct benefit from increasing calcium intake during lactation, and that physiological mechanisms operate to furnish calcium for breast-milk production.

The calcium and phosphorus intakes of rural Gambian women during pregnancy and lactation.

The Ca and P intakes of 148 pregnant and lactating women in a rural village in The Gambia, West Africa, have been estimated by direct weighing of food on a total of 4188 d. The Ca and P contents of local foods were determined by analysis of raw ingredients, snack foods and prepared dishes. Information about the contribution of mineral-rich seasonings was obtained. Efforts were made to discover unusual sources of Ca that might not be perceived as food by subject or observer. The main contributors to daily Ca intake were shown to be leaves, fish, cereals, groundnuts and local salt. Cow's milk accounted for only 5% of Ca intake. Unusual sources of Ca were discovered, namely baobab (Adansonia digitata) fruit and selected earths, but these were consumed infrequently and their contributions to Ca intakes were small. Cereals and groundnuts were the main sources of P. Ca and P intakes (mg/d) were shown to average 404 (SD 110) and 887 (SD 219) respectively. Seasonal changes in the availability of leaves, cereals and groundnuts resulted in variations in Ca and P intakes. The rainy season was associated with increased Ca intakes (by 16%) but decreased P consumption (by 15%). No difference was observed in Ca intake between pregnant and lactating women but P intake in lactation was 11% higher than that in pregnancy during the post-harvest season. The implications of these low Ca intakes require investigation.

A semi-automated micromethod for the determination of calcium and phosphorus in human milk.

A simple, semi-automated method for the analysis of calcium and phosphorus in small volumes of human milk is described. Samples are ashed, digested with dilute hydrochloric acid and assayed with commercially available kits on a centrifugal analyser. The precision and accuracy of the method are similar to those of standard manual methods using larger volumes of milk. Analysis of human milk for phosphorus without prior ashing and digestion gives observed concentrations only 30-40% of their true value.

Breast-milk amylase activity in English and Gambian mothers: effects of prolonged lactation, maternal parity, and individual variations.

Breast milk contains an amylase that may contribute to carbohydrate digestion in infants. The aim of our study was to determine whether mothers differ in their breast-milk amylase activity and whether the activity is maintained during prolonged lactation. This was investigated by measuring breast-milk amylase activity by hydrolysis of maltotetraose in 63 English mothers of parity 1-5 and 107 Gambian mothers of parity 1-12 who were at various stages of lactation (0.5-27 mo). Amylase was present in all samples and showed a great range of activity from 0.08 to 3.53 IU/mL. Amylase activities did not vary during a feed nor over 24 h, and each mother had a characteristic level of activity in her milk. Amylase activity was higher in the 1st trimester of lactation, and decreased by 35% (p less than 0.001) to a plateau at 6-27 mo. Gambian mothers of very high parity (parity 11-12) had 54% of the activity of primiparous mothers (p less than 0.001), after adjustment for stage of lactation. Using community data on milk volume, the estimated breast-milk amylase intake by breast-fed children was on the order of 800-1000 IU/24 h in the 1st trimester and 400 IU/24 h in the 2nd year of lactation. Individual measurements emphasized the great differences in this intake among children of the same age. Our study showed that breast milk is an important source of amylase both in developed and developing countries, but there are large variations in intake among children.