Serum concentrations of 25-hydroxyvitamin D in rickets of extremely premature infants

Sulfated vitamin D metabolites represent prominent roles in serum and in breastmilk of lactating women

BACKGROUND

Concentrations of vitamin D (VitD) and 25-hydroxyvitamin D (25OHD) in breastmilk are low despite the essential role of VitD for normal infant bone development, yet additional metabolic forms of vitamin D may be present. This study evaluates the contribution of sulfated vitamin D metabolites, vitamin D3-sulfate (VitD3-S) and 25-hydroxyvitamin D3-sulfate (25OHD3-S) for lactating women and assesses the response to high-dose VitD3 supplementation.

METHODS

Serum and breastmilk were measured before and after 28 days with 5000 IU/day VitD3 intake in 20 lactating women. Concentrations of VitD3-S and 25OHD3-S in milk, and 25OHD2, 25OHD3, 25OHD3-S, VitD3 and VitD3-S in serum were determined by mass spectrometry.

RESULTS

Baseline vitamin D status was categorized as sufficient (mean ± SD serum 25OHD3 69 ± 19 nmol/L), and both serum VitD3 and 25OHD3 increased following supplementation (p < 0.001). 25OHD3-S was 91 ± 19 nmol/L in serum and 0.47 ± 0.09 nmol/L in breastmilk. VitD3-S concentrations were 2.92 ± 0.70 nmol/L in serum and 6.4 ± 3.9 nmol/L in breastmilk. Neither sulfated metabolite significantly changed with supplementation in either serum or breastmilk.

CONCLUSIONS

Sulfated vitamin D metabolites have prominent roles for women during lactation with 25OHD3-S highly abundant in serum and VitD3-S distinctly abundant in breastmilk. These data support the notion that 25OHD3-S and VitD3-S may have physiological relevance during lactation and nutritional usage for nursing infants.

Vitamin requirements for term infants: considerations for infant formulae

OBJECTIVE

To provide the informed health professional with an up to date evaluation of the current thinking regarding requirements for vitamins in infant feeds. ESTABLISHING CRITERIA FOR ADEQUACY: Vitamin adequacy in the neonate is currently defined in terms of circulating levels of a vitamin or of the activity of a vitamin dependent enzyme in the erythrocytes. Although these measurements have their value there is a need to develop biochemical, physiological or clinical markers of well defined specific function. For some vitamins there is a risk of deleterious effects of very high intakes: risk of toxicity needs to be taken into consideration when making recommendations for inclusion in infant formulae. BREAST MILK AS THE 'GOLD STANDARD': Breast milk concentrations of vitamins have been used as the criteria of adequate intake by neonates. This may not always be justified. Greater consideration needs to be given to differences in bioavailability of vitamins from breast milk compared with formula feeds, of the influence of season, and of stage of lactation, on the stated composition.

EXPERIMENTAL APPROACHES

Animal studies have provided limited information regarding effects of different levels of intakes on current status indices in the neonatal period. There are few reports of randomized controlled studies into the effects of different levels of vitamins and these rely heavily on biochemical criteria of adequacy.

RECENT DEVELOPMENTS

The inclusion of beta-carotene into formula feeds for premature babies is an issue of current interest. What is the justification for this? Are there potential benefits for the term infant? Riboflavin deficiency in the period around weaning may affect the normal structural and functional development of the gastrointestinal tract; some of these effects may be permanent. RESEARCH TO BE DONE: A greater understanding of the absorption and metabolism of vitamins during infancy is required in order to help establish dietary requirements. The relative bioavailability of vitamins in human milk and formulae needs to be investigated. Criteria for vitamin adequacy should be extended to include measures of function. Information regarding the conversion factor from tryptophan to niacin in infancy would allow us to set niacin requirements with greater confidence. There is a particular lack of information about concentrations of biotin and pantothenic acid in breast milk and the relative biochemical status of infants receiving breast milk and formulae. Benefits of including beta-carotene into infant formulae need to be evaluated. The role of individual micronutrients in the structural and functional development of the gastrointestinal tract should be explored.

Vitamin D deficiency in pregnant women from a non-European ethnic minority population--an interventional study

OBJECTIVE

To determine the vitamin D status of pregnant women from non-European ethnic minorities in South Wales.

DESIGN

Prospective study.

SETTING

Llandough Hospital, Cardiff, South Wales.

SAMPLE

One hundred and sixty pregnant women from a non-European ethnic minority population in South Wales.

METHODS

Biochemical screening of vitamin D status was carried out at the first antenatal visit. Women found to be deficient in vitamin D were subsequently supplemented and vitamin D status was rechecked at delivery.

MAIN OUTCOME MEASURE

Vitamin D status at delivery.

RESULTS

Eighty of 160 women had a vitamin D level below 8 ng/mL at their first antenatal visit and were treated with oral vitamin D. Factors that could influence vitamin D status such as religion, fluency in English and dressing habits did not appear to have any effect, although a higher proportion of women who had lived in Britain for longer than three years had subnormal vitamin D levels. In 58 of those checked at delivery, the mean plasma vitamin D level increased from 6 to 11 ng/mL although the mean parathyroid hormone level was unchanged.

CONCLUSION

In view of the high incidence of subnormal vitamin D levels in women from ethnic minorities, we recommend biochemical screening of these women in early pregnancy, with subsequent supplementation where indicated.

Seasonal diminution of vitamin D stores in the United States. Can darker winters lead to lighter bones?

Recent reports indicate that many older Americans have inadequate vitamin D sources and little to no seasonal increase in their body stores. The attendant secondary hyperparathyroidism of incipient and subtle osteomalacia could weaken cortical bone and aggravate the osteoporotic process linked to aging. Increased awareness, by physicians and our elderly, of the importance of avoiding mild, seasonal or perennial vitamin D deficiency could lead to better implementation of vitamin D supplementation schedules.

Prematurity as a predictor of rickets in Shanghai infants

The association between prematurity and the prevalence of rickets was examined among 2,227 infants in Shanghai, China. The prevalence of rickets during subjects' first 18 months of life was 6.8% in boys and 4.6% in girls. Pre-term infants were more likely to have rickets than term (> or = 37 weeks gestation) infants, 9.4% versus 5.2%. Birth weight was inversely related to the prevalence of rickets, 15.8% in the < 2,500 g group, 7.1% in the 2,500-2,999 g group, 4.9% in the 3,000-3,499 g group, and 4.2% in the > or = 3,500 g group. After adjusting for covariates including sex, average family income and birth weight, the odds ratio for rickets in pre-term infants was 1.55 compared with term infants. The inverse relationship between birth weight and rickets remained significant after taking sex, family income and pre-term birth into account. In addition, infants of the lower income families were more likely to have rickets than those of higher income families.

Breast milk as a source of vitamins, essential minerals and trace elements

Human breast milk provides all of the vitamins and essential minerals and trace elements (micronutrients) that are required by the normal term infant, until weaning. With a few exceptions, excessive micronutrient supplies to the mother, or a moderate deficiency in her diet, do not greatly alter the supply to the infant. Thus, the infant is well-protected by maternal homeostatic processes, although the mechanisms of these are not yet well understood. Considerable progressive changes in concentration occur for some of the micronutrients during the course of lactation. Because the concentration of these nutrients, and of other substances that modify their absorption by the infant, such as binding proteins, differs considerably between human milk, animal milk and, hence, commercial milk formulae, there is great interest in the quantitative significance of micronutrient supplies, and their variability in breast milk, in the quest for improvement of commercial formulations. The aim of this review is to summarize the available information about the factors that determine breast milk contents of micronutrients.

Static bone histomorphometry in preterm and term babies

The nature and pathophysiology of the bone loss which occurs in term and especially preterm neonates are poorly understood, and it is unclear whether this neonatal osteopenia results from impaired bone formation or increased bone resorption. This study compared the static bone histomorphometry of preterm and term babies, employing iliac crest bone biopsy specimens obtained postmortem. All the babies died within the first 6 days of life and none had any clinical, biochemical or radiologic evidence of metabolic bone disease. The trabecular bone volume, as well as static parameters of bone formation (OV/TV, OV/BV, OS/BS, OB.S/BS) did not differ significantly in preterm and term babies. Although time-spaced tetracycline labelling could not be employed in the present study, evidence of rickets was not apparent. Parameters of bone resorption in preterm babies were, however, significantly higher (p = 0.01) than those of term babies, suggesting that increased bone resorption and not impaired formation, underlies the development of osteopenia in the preterm neonate.

High turnover osteopenia in preterm babies

Osteopenia is common in preterm babies, but its pathogenesis is uncertain. In this study bone density in babies was quantitated, postnatal bone mineralization compared to expected intrauterine bone mineralization and the pathogenesis of osteopenia investigated. Healthy babies (103 term, 76 preterm) were examined clinically, biochemically and radiologically the day after birth and at a time corresponding to expected full term gestation. Appendicular bone density was quantitated by magnification radiogrammetry, using the humeral cortical index (CI). The CI of preterm and term babies was similar the day after birth. In preterm babies elevated serum alkaline phosphatase and high urinary hydroxyproline indicated increased bone turnover. The CI of preterm babies at expected full term gestation was lower (p = 0.0001) than that of term babies at birth, implying that postnatal bone mineralization lagged behind expected intrauterine bone mineralization. Radiologic data suggested increased endosteal resorption rather than decreased bone formation. At expected full term gestation the preterm babies had higher serum alkaline phosphatase and urinary calcium, phosphate, c-AMP and hydroxyproline (p = 0.0001) than term babies at birth, and 15% had periosteal reactions. The biochemical as well as the radiologic data therefore indicated high turnover osteopenia in preterm babies. We conclude that postnatal bone mineralization in preterm babies lagged significantly behind expected intrauterine bone mineralization and that the osteopenia observed in preterm babies is caused by increased bone resorption and not by decreased bone formation. The cause(s) of this high turnover osteopenia, however, remains to be ascertained.

Role of plasma phosphate measurements in detecting rickets of prematurity and in monitoring treatment

Twice weekly plasma and urine measurements were made in 24 very low birth weight infants. Intravenous feeding was given whilst infants required respiratory support. Subsequently they received breast milk or formula milk with a vitamin D supplement of 400 U/day. Fourteen babies required intravenous feeding for more than 10 days. Six developed radiological rickets or severe osteoporosis, and these infants had plasma phosphate levels < 1.2 mmol/L on breast milk or < 1.8 mmol/L on formula milk. Babies without radiological rickets had plasma phosphate levels > 1.2 mmol/L on breast milk and > 1.8 mmol/L in all but one on formula milk. Successful treatment of rickets was associated with a rise in plasma phosphate to the above levels. Untimed urine calcium and phosphate concentrations expressed as creatinine ratios were not helpful in detecting babies with rickets, but may be useful in monitoring therapy.

Serum vitamin D metabolites in very low birth weight infants with and without rickets and fractures

Seventy-one very low birth weight (less than or equal to 1500 gm) infants were studied to determine the sequential changes in serum vitamin D metabolite concentrations between infants with and without radiographically documented rickets, fractures, or both (R/F). Usual intake of vitamin D included 20 IU/kg/day from parenteral nutrition or 400 IU/day supplementation with enteral feeding. Radiographs of both forearms and serum samples were obtained at 3, 6, 9, and 12 months. Twenty-two infants had R/F. At 3 months, significantly lower mean (+/- SEM) serum phosphorus levels (4.5 +/- 0.4 vs 6.1 +/- 0.2 mg/dl), higher 1,25-dihydroxyvitamin D (1,25-[OH]2D) concentrations (96 +/- 5 vs 77 +/- 4 pg/ml), and higher free 1,25-(OH)2D index (1,25-[OH]2D:vitamin D binding protein ratio; 5.2 +/- 0.3 x 10(5) vs 4.0 +/- 0.2 x 10(5] were found in the R/F group. These values returned to normal and were similar between groups on subsequent measurements. Serum calcium, magnesium, and 25-hydroxyvitamin D (25-OHD) concentrations were normal and similar between groups. In both groups, serum vitamin D binding concentrations increased initially but remained stable and normal beyond 6 months. We conclude that in very low birth weight infants with R/F, the vitamin D status (as indicated by serum 25-OHD concentrations) is normal, and that lowered serum phosphorus levels, higher serum 1,25-(OH)2D levels, and a higher free 1,25-(OH)2D index support the thesis that mineral deficiency (especially of phosphorus) may be important in the pathogenesis of R/F in small preterm infants.

Vitamin D metabolism, mineral homeostasis, and bone mineralization in term infants fed human milk, cow milk-based formula, or soy-based formula

The purpose of this study was to evaluate mechanisms of mineral homeostasis and mineralization in term infants with recommended vitamin D intakes. Infants fed human milk (nine), cow milk-based formula (11), or soy-based formula (11) were studied at 2 weeks and at 2, 4, 6, 9, and 12 months of age. While receiving 400 IU of vitamin D, all infants maintained serum vitamin D concentrations higher or equal to normal adult concentrations, and serum 25-hydroxyvitamin D levels were maintained at or above normal adult levels. Serum 1,25-dihydroxyvitamin D concentrations were higher than those of adults in the formula-fed but not in the human milk-fed infants. Serum calcium and phosphorus values were similar in all groups; however, urine phosphorus excretion and urine calcium excretion were adjusted to intakes. Serum parathyroid hormone values were normal in all groups. Bone mineral content significantly increased with age similarly in all groups; however, an apparent plateau occurred at 6 months of age in all groups. Bone width steadily increased with age. Taken as a whole, these data suggest that the vitamin D-sufficient term infant fed human milk, cow milk-based formula, or the soy-based formula studied can regulate mineral metabolism within acceptable physiologic limits to attain similar levels of serum minerals and bone mineral content.

Phosphorus deficiency syndrome in very low birth weight infants

Inadequate dietary phosphorus intake is a contributing factor to the occurrence of metabolic bone disease in very low birth weight infants. This article reviews the clinical presentation and the pathophysiology of the phosphorus deficiency syndrome in premature infants. Recommendations for therapy and prevention of phosphorus deficiency are presented.

Calcium homeostasis in premature infants and treatment of early hypocalcaemia by 1,25-dihydroxycholecalciferol

We studied calcium homeostasis and the serum calcium response to oral 1,25-dihydroxycholecalciferol [1,25 (OH)2D3] at a low pharmacological dosage of 0.1 microgram/kg daily in 14 early hypocalcaemic asymptomatic neonates. Seven hypocalcaemic neonates were not treated. In hypocalcaemic neonates serum PTH levels were normal, the urinary C-AMP response after PTH stimulation was poor and plasma 1,25 (OH)2D3 was low. Treatment with 1,25(OH)2D3 resulted in a rapid increase of serum calcium. The increase was more rapid in neonates treated with 1,25(OH)2D3 than in untreated subjects. A similar result was obtained in one of a pair of identical twins. These results suggest that a low dose of 1,25(OH)2D3 is effective in treating neonatal hypocalcaemia. However, the response was delayed for 48 h. The reason for this delay is not clear.

Absorption, dosage, and effect on mineral homeostasis of 25-hydroxycholecalciferol in premature infants: comparison with 400 and 800 IU vitamin D2 supplementation

Because the efficiency of vitamin D absorption or hepatic uptake and 25-hydroxylation appears decreased in very premature infants, the routine use of 25-hydroxycholecalciferol (25-OHD3) supplementation has been suggested. Absorption studies of a 3 micrograms/kg orally administered dose of 25-OHD3 showed peak serum 25-hydroxyvitamin D2 and -vitamin D3 (25-OHD) concentrations at 4 to 8 hours similar in timing but of lesser magnitude to those seen in adults. Administration of 1 microgram/kg birth weight/day of 25-OHD3 corrected moderately low, but not very low serum (25-OHD) concentrations, and 2 micrograms/kg BW/day resulted in rapid and sustained increase in serum 25-OHD. Administration of 800 IU ergocalciferol (D2) also produced significantly higher serum 25-OHD concentrations than those in infants given 400 IU vitamin D2, but increases in serum 25-OHD were more gradual than in infants given 25-OHD3. In treatment trials with infants weighing less than 1500 gm, those given 800 IU D2, compared with those given 400 IU D2, had higher serum calcium concentrations and less frequent moderate or severe hypomineralization. Infants given 2 micrograms/kg BW 25-OHD3 had a significant increase in serum phosphorus values, but a decrease in serum calcium and magnesium concentrations, and parathyroid hormone also was suppressed to low normal values. The frequency of moderate to severe hypomineralization remained the same as in infants given 400 IU D2. In a subgroup of infants, serum 1,25-dihydroxyvitamin D was elevated over adult values, both in infants given 25-OHD3 (68.5 +/- 8.4 pg/ml) and in infants given vitamin D2 (60 +/- 6.7 pg/ml). Serum vitamin D concentrations were undetectable in four of six infants receiving 25-OHD3, but were elevated (5 to 31 ng/ml) in four infants receiving vitamin D2. Although 800 to 1000 IU D2 can be recommended as routine vitamin D supplementation in very premature infants fed standard formula, the use of 25-OHD3 requires further study.

Mineral homeostasis in very premature infants: serial evaluation of serum 25-hydroxyvitamin D, serum minerals, and bone mineralization

This study was designed to evaluate the role of vitamin D sufficiency, as reflected in serum 25-hydroxyvitamin D (25-OHD) concentrations, on serum minerals and bone mineralization in very premature infants. Seventy-two infants (mean +/- SD gestation 30.1 +/- 2.5 weeks, mean +/- SD birth weight 1178 +/- 278 gm) were observed serially for the first 3 months of life. Mean serum calcium and phosphorus values, but not magnesium, remained low prior to 12 weeks. The percentage of infants with moderate to severe hypomineralization was 75% at 3 weeks, 55% at 6 weeks, 54% at 9 weeks, and 15% at twelve weeks. Low serum calcium and phosphorus values, high alkaline phosphatase activity, and moderate-severe hypomineralization were more frequent in infants weighing less than 1000 gm and in those with lower mineral intake. With a 400 IU vitamin D supplement, 45% of infants could maintain an initially normal serum 25-OHD concentration or increase low concentrations, whereas 55% had falling or persistently low (less than or equal to 15 ng/ml) 25-OHD concentrations. Birth weight and mineral intakes were comparable in these two groups, yet the group with the lower serum 25-OHD concentration had lower serum calcium and higher alkaline phosphatase values, and a higher percentage of moderate to severe hypomineralization. Regardless of birth weight, mineral intake, or 25-OHD concentration, increases in serum calcium and phosphorus values and in mineralization were seen at postconception term (12 weeks in most infants, nine weeks in those weighing 1250 to 1600 gm). At 12 weeks of age, but not before, serum 25-OHD concentration was directly correlated with serum calcium (r = 0.47, P less than 0.01) and serum phosphorus (r = 0.47, P less than 0.01) and inversely correlated with alkaline phosphatase values (r = -0.71, P less than 0.01). Mineral availability and 25-OHD sufficiency both appear to be important and to act synergistically, with neither totally compensating for the other.

Plasma concentrations of vitamin D metabolites in a case of rickets of prematurity

Rickets was diagnosed in an extremely low-birthweight infant 16 weeks after birth. She had a normal plasma concentration of 25-hydroxyvitamin D, a relatively low level of 24,25-dihydroxyvitamin D, and a markedly elevated 1,25-dihydroxyvitamin D level compared with adult standards. The plasma concentrations of the vitamin D metabolites were, however, indistinguishable from those of healthy preterm infants who received a similar diet of human milk and vitamins. The results indicate that rickets was not caused by vitamin D deficiency or by abnormal vitamin D metabolism, but by calcium and/or phosphate deficiency, and that the calcium and phosphorous content of human milk may be inappropriately low for very low-birthweight infants.

Vitamin D nutritional status of premature infants supplemented with 500 IU vitamin D2 per day

The vitamin D nutritional status of premature infants was assessed by determining plasma 25-hydroxyvitamin D concentrations before and during supplementation with 500 IU vitamin D2 per day. Fifty-one samples were collected from 25 healthy infants fed breast milk and a vitamin D3 fortified formula. Gestational age was 32.2 +/- 2.4 weeks (mean +/- 1 SD). 25-hydroxyvitamin D levels before supplementation correlated well with maternal values (r = 0.81). The infants' mean plasma concentration increased from 30.6 +/- 13.7 nmol/l (mean +/- 1 SD) after birth to 46.3 +/- 10.5 nmol/l after 9 +/- 1 days (p less than 0.0025), and to 65.3 +/- 16.6 nmol/l after 37 +/- 10 days of vitamin D2 treatment (p less than 0.0005). 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 were determined separately, and it appeared that the rise was accounted for by the D2 fraction while 25-hydroxyvitamin D3 concentrations were unchanged. The results demonstrate that vitamin D2 is well absorbed and hydroxylated in the 25 position by premature infants free of associated disease, and that a supplementation of 500 IU per day in addition to breast milk and a regular vitamin D fortified formula is adequate to rapidly establish 25-hydroxyvitamin D levels within the normal adult range.

Understanding parenteral nutrition. A basis for neonatal nursing care

The challenge in meeting the caloric and metabolic demands of infants who are critically ill, debilitated, or neurophysically immature is discussed. Advances in nutrition that have greatly improved neonatal survival are presented. Intravenous nutrition is presented as an appropriate mode of therapy to provide or supplement nutritional support in neonates who cannot derive all the requirements from oral feedings.

Neonatal rickets in one of identical twins

We report a case of rickets in one of identical low birthweight twin infants. Plasma 25-hydroxycholecalciferol concentrations were normal in both infants; there was good clinical response to 1-α hydroxycholecalciferol. We suggest that there was a delay in maturation of renal 25-hydroxycholecalciferol-1α hydroxylase enzyme.

Serum calcitonin concentrations in premature infants during the first 12 weeks of life

Twenty-eight premature infants of mean gestation 30.9 +/- 2.5 weeks and mean birth weight 1175 +/- 206 g had repeated serum calcitonin concentrations determined over the first 12 weeks of life. Serum calcitonin concentrations slowly fell but remained elevated even at 12 weeks of age [normal adult = 71 +/- 48, 1 week (N = 15) = 327 +/- 167, 3 week (N = 23) = 270 +/- 129, 6 week (N = 16) = 249 +/- 154, 9 week (N = 13) = 214 +/- 108, 12 week (N = 12) = 174 +/- 11]. Throughout this period, serum total calcium was normal or low (8.4 +/- .8-9.3 +/- 1.0). Serum phosphorus was normal or low (6.0 +/- 1.4-6.5 +/- 1.0), and serum magnesium was normal (1.7 +/- 0.24-1.8 +/- 0.34). The reason for the sustained elevation of serum calcitonin in these very small, sick, premature infants in unclear.

Do breast and bottle fed babies require vitamin supplements?

In the present stage of knowledge, the following approach to vitamin supplementation seems reasonable. Breast-fed full-term infants should be supplemented with vitamin D (400 I.U./day). Supplementation of bottle-fed infants will depend upon the vitamin content of the formula which is being used. Pre-term and LBW infants may need higher amounts of vitamin D (800-1 000 I.U./day) and should be supplemented with vitamin E (1-2 I.U./day), C (50 mg/day), B6 (30-60 mcg/day) and folic acid (50-100 mcg/day) when they are being fed formulas with high amounts of PUFA and proteins or with iron. Multivitamin supplementation appears to be acceptable for infants of very low birth weight (less than 1 500 g) until they reach a body weight of at least 2 000 grams or a caloric intake of 300 kcal/day. Finally, the present routine of administering 0.5-1.0 mg of vitamin K at birth to all infants should be continued.

Critical vitamins for low birthweight infants

All vitamins are "critical" by definition for the growing infant. However, some of them are particularly relevant to the preterm or low birthweight (LBW) infant in whom a deficiency can occur more frequently than in a full-term newborn. In LBW infants vitamin deficiency may develop due to (1) low body stores at birth, (2) low intake, (3) limited absorption, (4) increased need or utilization, (5) presence of certain clinical conditions. The first reason concerns all lipid-soluble vitamins, and particularly vitamin E and K, which cross the placenta with some difficulty. Among hydrosoluble vitamins, cord-blood levels of vitamin B6 have been shown to be abnormally low in preterm infants. Low intake can occur because of low vitamin levels in milk or because of delayed and/or insufficient feeding. Limited intestinal absorption of vitamins in LBW infants has only been demonstrated for vitamin E and folic acid. The rapid post-natal growth may lead to increased vitamin utilization. In some clinical conditions particularly high intakes of certain vitamins are indicated. In our opinion, the really "critical" vitamins in LBW infants are vitamin D, E, K and folic acid, for which routine supplementation can be recommended, and possibly vitamins C and B6 under special circumstances.

Skeletal changes in preterm infants

The skeletal changes in 19 very low birthweight infants (less than 1500 g) were observed from birth to 10 weeks, by means of clinical, biochemical, and radiological techniques. All infants were receiving a supplement of 800 IU vitamin D a day from age 2 weeks. None of the infants showed any specific physical sign of rickets during the period of study. Six infants showed radiological evidence of skeletal demineralisation; 1 of these had severe changes of rickets and 1 had both rickets and fractures. These 6 infants were of shorter gestational periods and lower birthweights than the infants not showing radiological changes. They tended to have more clinical problems and to reach a predetermined volume of feeds (160 ml/kg a day) later than the unaffected infants. Serum alkaline phosphatase values were significantly higher at 5 weeks in the infants with abnormal radiographs than in those without. There were no significant differences between the two groups in relation to serum calcium, inorganic phosphate, 25 hydroxyvitamin D, and immunoreactive parathyroid hormone. The pathogenesis of the skeletal lesions of very low birthweight infants remains unknown.

Rickets in premature infants receiving parenteral nutrition: a case report and review of the literature

There is a multifactorial etiology for rickets in premature infants receiving total parenteral nutrition. As an example of this, we describe a premature infant fed almost exclusively parenterally for the first 8 months of life who developed biochemical and radiologic evidence of rickets despite receiving vitamin D, calcium, and phosphorus at presently recommended levels. From our experience and a review of previous literature, there appears to be considerable uncertainty regarding the intravenous requirements of calcium, phosphorus, and vitamin D, particularly in low-birth weight infants. Therefore, measurements of serum 25-hydroxyvitamin D levels, vitamin D, and mineral intakes, and calcium and phosphorus excretion might be clinically useful for monitoring premature infants receiving total parenteral nutrition. Further research delineating more precisely the vitamin D, calcium, and phosphorus requirements of such infants is also suggested.

Elevated serum 1,25 dihydroxyvitamin D concentrations in rickets of very low-birth-weight infants

Elevated 1,25 dihydroxyvitamin D concentrations were found in five VLBW infants who developed rickets at two to three months postnatal age or term postconceptual age; 25 hydroxyvitamin D concentrations were low. Bone mineralization was found to be extremely low as measured by infant-adapted direct photon absorptiometry. After treatment with a formula supplemented with additional Ca and P, there was a rapid improvement in bone mineralization with a concomitant decrease of 1,25(OH)2D to normal adult values, whereas 250HD values increased and parathyroid hormone values decreased. In the VLBW infants studied, we suggest that rickets may be caused by Ca and P deficiency rather than by a deficiency of vitamin D metabolism.

Late evolution of serum immunoreactive parathyroid hormones, calcitonin and plasma 25-hydroxy cholecalciferol concentrations in very low birthweight infants

The plasma concentrations of 25-hydroxycholecalciferol (25-OH-CC), immunoreactive parathyroid hormone (iPTH) and calcitonin (iCT) were measured at the age of 30 and 66 days in thirteen preterm neonates (birthweight: 970 to 1300 g). At the age of 30 days when all infants were fed only with breast milk (BM) serum iCT and iPTH levels were normal. During the second month 7 infants were fed with BM only (control group) and 6 infants were supplemented with formula (supplemented group). At the age of 66 days, mean +/- S.D. serum iPTH concentration was higher in the supplemented group than in the control group: 169 +/- 79 vs. 60 +/- 33 microliterEq/ml (p less than 0.01). Serum iCT levels remained undetectable (less than 150 pg/ml) in both groups. Plasma 25-OH-CC concentrations were normal and similar in both groups. Serum iPTH concentrations were positively correlated with phosphorus intake and negatively correlated with calcium intake from BM only. The results suggest that secondary hyperparathyroidism can be detected in very low birthweight infants supplemented with a formula, probably because of a phosphorus load or decreased intestinal absorption of calcium.

Etiologic factors in rickets of very low-birth-weight infants

The incidence of rickets was found to be 32% (39/125) in a retrospective review of consecutive survivors of very low birth weight in whom serial radiographic and biochemical data were obtained. A higher proportion of these infants were black, had a greater initial weight loss, and had a longer hospitalization; there was a prevalence of births in the spring. Soy formula, supplemented with calcium and vitamin D but not phosphorus, was used predominantly in both groups; cumulative calcium, phosphorus, vitamin D, and caloric intakes were the same. We believe that the etiology of rickets in VLBW infants is multifactorial; however, nutritional deficiency is of central importance. Soy isolate formula, as well as human milk and many other commercially available formulas, do not provide sufficient calcium and phosphorus to keep pace with rates of intrauterine accretion. Supplementation with calcium, phosphorus, and vitamin D, beginning as soon as possible after birth, is indicated.