Vitamin D deficiency or resistance and hypophosphatemia.

Vitamin D is mainly produced in the skin (cholecalciferol) by sun exposure while a fraction of it is obtained from dietary sources (ergocalciferol). Vitamin D is further processed to 25-hydroxyvitamin D and 1,25-dihydroxy vitamin D (calcitriol) in the liver and kidneys, respectively. Calcitriol is the active form which mediates the actions of vitamin D via vitamin D receptor (VDR) which is present ubiquitously. Defect at any level in this pathway leads to vitamin D deficient or resistant rickets. Nutritional vitamin D deficiency is the leading cause of rickets and osteomalacia worldwide and responds well to vitamin D supplementation. Inherited disorders of vitamin D metabolism (vitamin D-dependent rickets, VDDR) account for a small proportion of calcipenic rickets/osteomalacia. Defective 1α hydroxylation of vitamin D, 25 hydroxylation of vitamin D, and vitamin D receptor result in VDDR1A, VDDR1B and VDDR2A, respectively whereas defective binding of vitamin D to vitamin D response element due to overexpression of heterogeneous nuclear ribonucleoprotein and accelerated vitamin D metabolism cause VDDR2B and VDDR3, respectively. Impaired dietary calcium absorption and consequent calcium deficiency increases parathyroid hormone in these disorders resulting in phosphaturia and hypophosphatemia. Hypophosphatemia is a common feature of all these disorders, though not a sine-qua-non and leads to hypomineralisation of the bone and myopathy. Improvement in hypophosphatemia is one of the earliest markers of response to vitamin D supplementation in nutritional rickets/osteomalacia and the lack of such a response should prompt evaluation for inherited forms of rickets/osteomalacia.

Feline precision medicine using whole-exome sequencing identifies a novel frameshift mutation for vitamin D-dependent rickets type 2.

OBJECTIVES: A 14-week-old female domestic longhair kitten presented with shifting lameness and disproportionately smaller size compared with a co-housed littermate. METHODS: Hematology and serum biochemical testing were conducted to investigate causes for delayed growth, and radiographs of the appendicular skeleton were obtained. RESULTS: The afflicted kitten had marked hypocalcemia, mild hypophosphatemia and substantial elevations in alkaline phosphatase activity, as well as pathognomonic radiographic findings consistent with rickets. Skeletal changes and hypocalcemia prompted testing of concentrations of parathyroid hormone (PTH) and vitamin D metabolites. Endocrine testing demonstrated significant increases in serum concentrations of PTH and 1,25-dihydroxycholecalciferol (calcitriol), supporting a diagnosis of vitamin D-dependent rickets type 2. Provision of analgesia, supraphysiologic doses of calcitriol and calcium carbonate supplementation achieved normalization of the serum calcium concentration and restoration of normal growth, although some skeletal abnormalities persisted. Once skeletally mature, ongoing calcitriol supplementation was not required. Whole-exome sequencing (WES) was conducted to identify the underlying DNA variant. A cytosine deletion at cat chromosome position B4:76777621 in VDR (ENSFCAT00000029466:c.106delC) was identified and predicted to cause a stop codon in exon 2 (p.Arg36Glufs*18), disrupting >90% of the receptor. The variant was unique and homozygous in this patient and absent in the sibling and approximately 400 other cats for which whole-genome and whole-exome data were available. CONCLUSIONS AND RELEVANCE: A unique, heritable form of rickets was diagnosed in a domestic longhair cat. WES identified a novel frameshift mutation affecting the gene coding for the vitamin D3 receptor, determining the likely causal genetic variant. Precision medicine techniques, including whole-exome and whole-genome sequencing, can be a standard of care in cats to identify disease etiologies, and to target therapeutics and personalize treatment.

Pitfalls in the Diagnosis of Primary Hyperparathyroidism in a Sudanese Adolescent Boy; a case disguised as rickets.

BACKGROUND: Juvenile primary hyperparathyroidism (PHPT) is a rare endocrine disease. Its diagnosis might be masked by clinical, biochemical, and radiological features of rickets. CASE PRESENTATION: A 12-year-old Sudanese boy presented with progressive lower limbs deformity and difficulty in walking for six months. It was associated with fatigability, poor appetite, and generalized bone pain. On examination, he was thin, disproportionately short and pubertal, and had bilateral genu valgum deformity. X-rays showed osteopenia and signs of rickets. Biochemical workup revealed mildly elevated serum calcium, low phosphate, high alkaline phosphatase, and high parathyroid hormone with low 25-hydroxy vitamin D3. Celiac screening, liver function test and renal profile were normal. Serum calcium rose dramatically after vitamin D therapy. Genetic testing was negative for CYP2R1 and MEN1 genes. Ultrasound neck showed left inferior parathyroid adenoma which was surgically excised. Histopathology confirmed the diagnosis of parathyroid adenoma. Postoperatively, he had hypocalcemia which was treated with calcium and alfacalcidol. Corrective surgery is planned for the genu valgum deformity which markedly improved after parathyroidectomy. CONCLUSION: Although PHPT is extremely rare in the young population, it should be considered in patients with rickets and elevated serum calcium at baseline or after initiating vitamin D therapy.

Not all the bowlegs is rickets! (a case report).

Bowing of the legs is common in childhood. Most times it is considered to be rickets without considering other possibilities. Blount´s disease is a close differential diagnosis which is developmental deformity characterized by intorsion of tibia leading to varus angulation. This case report aims to encourage pediatricians to expand their vision and consider other possibilities when a case of bowing of legs is encountered. Here we report a case of a four-year-old boy with bowing of both legs noticed first at 2.5 years of age. There was no history suggestive of trauma. Development of the child was age appropriate in all domains. He was receiving treatment for rickets for 1.5 years in form of oral vitamin D3 and calcium supplementations. He had no other clinical signs of rickets like frontal bossing, widening of wrists, and rachitic rosary except bowing of legs. His biochemical parameters did not show any alterations that would support the diagnosis of rickets. Weight-bearing radiographs of lower limbs showed medial intorsion of bilateral tibia with metaphyseo-diaphysial angle to be 25º on the right side and 20º on the left side, which was beyond the physiological normal angulation, therefore he was diagnosed as a case of Blount´s disease, stage III as per Langenskiöld classification. All the bow legs is not always rickets in pediatric practice. Therefore, various differential diagnoses should be kept in mind as early diagnosis and intervention can change a child´s life.

Vitamin D: sources, physiological role, biokinetics, deficiency, therapeutic use, toxicity, and overview of analytical methods for detection of vitamin D and its metabolites.

Vitamin D has a well-known role in the calcium homeostasis associated with the maintenance of healthy bones. It increases the efficiency of the intestinal absorption of dietary calcium, reduces calcium losses in urine, and mobilizes calcium stored in the skeleton. However, vitamin D receptors are present ubiquitously in the human body and indeed, vitamin D has a plethora of non-calcemic functions. In contrast to most vitamins, sufficient vitamin D can be synthesized in human skin. However, its production can be markedly decreased due to factors such as clothing, sunscreens, intentional avoidance of the direct sunlight, or the high latitude of the residence. Indeed, more than one billion people worldwide are vitamin D deficient, and the deficiency is frequently undiagnosed. The chronic deficiency is not only associated with rickets/osteomalacia/osteoporosis but it is also linked to a higher risk of hypertension, type 1 diabetes, multiple sclerosis, or cancer. Supplementation of vitamin D may be hence beneficial, but the intake of vitamin D should be under the supervision of health professionals because overdosing leads to intoxication with severe health consequences. For monitoring vitamin D, several analytical methods are employed, and their advantages and disadvantages are discussed in detail in this review.

Rickets guidance: part II-management.

Here, we discuss the management of different forms of rickets, including new therapeutic approaches based on recent guidelines. Management includes close monitoring of growth, the degree of leg bowing, bone pain, serum phosphate, calcium, alkaline phosphatase as a surrogate marker of osteoblast activity and thus degree of rickets, parathyroid hormone, 25-hydroxyvitamin D3, and calciuria. An adequate calcium intake and normal 25-hydroxyvitamin D3 levels should be assured in all patients. Children with calcipenic rickets require the supplementation or pharmacological treatment with native or active vitamin D depending on the underlying pathophysiology. Treatment of phosphopenic rickets depends on the underlying pathophysiology. Fibroblast-growth factor 23 (FGF23)-associated hypophosphatemic rickets was historically treated with frequent doses of oral phosphate salts in combination with active vitamin D, whereas tumor-induced osteomalacia (TIO) should primarily undergo tumor resection, if possible. Burosumab, a fully humanized FGF23-antibody, was recently approved for treatment of X-linked hypophosphatemia (XLH) and TIO and shown to be superior for treatment of XLH compared to conventional treatment. Forms of hypophosphatemic rickets independent of FGF23 due to genetic defects of renal tubular phosphate reabsorption are treated with oral phosphate only, since they are associated with excessive 1,25-dihydroxyvitamin D production. Finally, forms of hypophosphatemic rickets caused by Fanconi syndrome, such as nephropathic cystinosis and Dent disease require disease-specific treatment in addition to phosphate supplements and active vitamin D. Adjustment of medication should be done with consideration of treatment-associated side effects, including diarrhea, gastrointestinal discomfort, hypercalciuria, secondary hyperparathyroidism, and development of nephrocalcinosis or nephrolithiasis.

The health effects of vitamin D supplementation: evidence from human studies.

Vitamin D supplementation can prevent and cure nutritional rickets in infants and children. Preclinical and observational data suggest that the vitamin D endocrine system has a wide spectrum of skeletal and extra-skeletal activities. There is consensus that severe vitamin D deficiency (serum 25-hydroxyvitamin D (25OHD) concentration <30 nmol/l) should be corrected, whereas most guidelines recommend serum 25OHD concentrations of >50 nmol/l for optimal bone health in older adults. However, the causal link between vitamin D and many extra-skeletal outcomes remains unclear. The VITAL, ViDA and D2d randomized clinical trials (combined number of participants >30,000) indicated that vitamin D supplementation of vitamin D-replete adults (baseline serum 25OHD >50 nmol/l) does not prevent cancer, cardiovascular events, falls or progression to type 2 diabetes mellitus. Post hoc analysis has suggested some extra-skeletal benefits for individuals with vitamin D deficiency. Over 60 Mendelian randomization studies, designed to minimize bias from confounding, have evaluated the consequences of lifelong genetically lowered serum 25OHD concentrations on various outcomes and most studies have found null effects. Four Mendelian randomization studies found an increased risk of multiple sclerosis in individuals with genetically lowered serum 25OHD concentrations. In conclusion, supplementation of vitamin D-replete individuals does not provide demonstrable health benefits. This conclusion does not contradict older guidelines that severe vitamin D deficiency should be prevented or corrected.

Vitamin D deficiency, supplementation and testing: have we got it right in New Zealand?

BACKGROUND: Severe prolonged vitamin D deficiency can cause rickets or osteomalacia. Both can be prevented by sunshine exposure or vitamin D supplementation. Although New Zealand guidance does not recommend vitamin D supplementation for the general population, it can be considered for individuals at risk of vitamin D deficiency. Routine measurement of 25-hydroxyvitamin D (25OHD) is also considered unnecessary. METHODS: We investigated the rates of vitamin D supplementation, rickets and osteomalacia in New Zealand, and of 25OHD results in Auckland, over the last two decades. RESULTS: Vitamin D prescriptions increased 14-fold, from 86,295/year to 1,215,507/year, between 2003 and 2019, with medication costs alone in 2019 being >$1 million. Despite these changes, the annual prevalence of hospital admissions for rickets, osteomalacia and unspecified vitamin D deficiency remained low and stable (10-20/year). 25OHD concentrations increased between 2002 and 2003 and between 2009 and 2019, and in the later time-period, 25OHD tests mainly identified individuals without vitamin D deficiency (40-50% >75nmol/L, 65-70% >50nmol/L and only 7-12.5% <25nmol/L). CONCLUSIONS: Osteomalacia and rickets persist at low rates despite widespread, increasingly costly vitamin D supplementation and testing, which largely identifies individuals without vitamin D deficiency. These results suggest that vitamin D guidance and practice in New Zealand should change.

Monitoring response to conventional treatment in children with XLH: Value of ALP and Rickets Severity Score (RSS) in a real world setting.

INTRODUCTION: X-linked hypophosphataemia (XLH) is conventionally managed with oral phosphate and active vitamin D analogues. OBJECTIVES: To evaluate long term treatment response by assessing biochemical disease activity [serum alkaline phosphatase (ALP)], radiological rickets severity score (RSS), growth and morbidity in patients with XLH on conventional therapy and assess the correlation between serum ALP and RSS. METHODS: XLH patients from 3 UK tertiary centres with ≥3 radiographs one year apart were included. Data was collected retrospectively. The RSS was assessed from routine hand and knee radiographs and ALP z scores were calculated using age-specific reference data. RESULTS: Thirty-eight (male = 12) patients met the inclusion criteria. The mean ± SD knee, wrist and total RSS at baseline (median age 1.2 years) were 2.0 ± 1.2, 1.9 ± 1.2 and 3.6 ± 1.3 respectively; and at the most recent clinic visit (median age 9.0 years, range 3.3-18.9) were 1.6 ± 1.0, 1.0 ± 1.0 and 2.5 ± 1.5 respectively. The mean ± SD serum ALP z scores at baseline and the most recent visit were 4.2 ± 2.3 and 4.0 ± 3.3. Median height SDS at baseline and most recent visit were -1.2 and -2.1 (p = 0.05). Dental abscess, craniosynostosis, limb deformity requiring orthopaedic intervention and nephrocalcinosis were present in 31.5%, 7.9%, 31.6% and 42.1% of the cohort respectively. There was no statistically significant (p > 0.05) correlation between ALP z scores and knee (r = 0.07) or total (r = 0.12) RSS. CONCLUSIONS: Conventional therapy was not effective in significantly improving biochemical and radiological features of disease. The lack of association between serum ALP and rickets severity on radiographs limits the value of ALP as the sole indicator of rickets activity in patients receiving conventional therapy.

Calcium repletion to rats with calcipenic rickets fails to recover bone quality: A calcipenic "memory".

Calcipenic rickets is prevalent in underprivileged children in developing countries. Calcipenic rickets resulting from dietary calcium (Ca) deficiency decreases bone mass and deteriorates bone microstructure in humans. The effect of dietary Ca replenishment (CaR) on rachitic bones in animal models depends on the amount, critical period and duration of replenishment, however, the extent of recovery in various bone parameters including bone quality remains unclear. We investigated the effect of CaR in rat skeleton after inducing calcipenic rickets. Female SD rats (postnatal 28 days/P28) were rendered calcipenic by feeding calcium deficient (CaD) diet (0.1% Ca) till P70 while control SD rats were fed Ca sufficient diet (0.8% Ca). At P70, calcipenic rats were switched to 0.8% Ca diet till P150 for one group and P210 for another group (endpoint). The CaD groups received 0.1% Ca diet throughout the study (P210). In the CaD groups, serum Ca and phosphate, and bone mineral density (BMD) were significantly decreased whereas serum alkaline phosphatase (ALP), iPTH and CTX-1 were increased compared to age-matched controls. Moreover, at the endpoint, the CaD group had reduced bone mass, surface referent bone formation parameters, tissue mineralization and strength accompanied by the increased osteoid thickness and microarchitectural decay (measured by trabecular geometric parameters) with poor crystal packing. The CaR group showed complete recovery in serum Ca, iPTH, ALP and CTX-1, and BMD, however, the bone quality parameters including bone strength, microarchitectural decay, tissue mineralization, and crystallinity were incompletely restored. Decreased surface referent bone formation and increased unmineralized bones (osteoid) indicative of osteomalacia were also observed in the CaR group at P210 compared with control despite prolonged replenishment. We conclude that a prolonged Ca repletion following the induction of calcipenic rickets in rats although shows the recovery of biochemical measures of bone metabolism and bone mass, however, the bone quality remains compromised. This suggests that a "memory" of calcipenia occurring at the early growth stage persists in the skeleton of adult rats despite a prolonged Ca replenishment.

[MODERN ISSUES OF D-VITAMIN SIGNIFICANCE IN DEVELOPMENT OF FULERUM-MOVE DEVICES OF INFANTS, CHILDREN AND ADOLESCENTS ( REVIEW)].

The purpose of this review is the study of literature for the current data on the metabolism of vitamin D and its role in development of bone tissue in children. The role of the main marker enabling assessing 25(OH)D concentration in the body the reference values has been analyzed. Summarizing the literature data, we may say that vitamin D and calcium deficiencies are common worldwide, causing nutritional rickets and osteomalacia, which have a mayor impact on health of infants, children and adolescents.

Skeletal and Extraskeletal Actions of Vitamin D: Current Evidence and Outstanding Questions.

The etiology of endemic rickets was discovered a century ago. Vitamin D is the precursor of 25-hydroxyvitamin D and other metabolites, including 1,25(OH)2D, the ligand for the vitamin D receptor (VDR). The effects of the vitamin D endocrine system on bone and its growth plate are primarily indirect and mediated by its effect on intestinal calcium transport and serum calcium and phosphate homeostasis. Rickets and osteomalacia can be prevented by daily supplements of 400 IU of vitamin D. Vitamin D deficiency (serum 25-hydroxyvitamin D <50 nmol/L) accelerates bone turnover, bone loss, and osteoporotic fractures. These risks can be reduced by 800 IU of vitamin D together with an appropriate calcium intake, given to institutionalized or vitamin D-deficient elderly subjects. VDR and vitamin D metabolic enzymes are widely expressed. Numerous genetic, molecular, cellular, and animal studies strongly suggest that vitamin D signaling has many extraskeletal effects. These include regulation of cell proliferation, immune and muscle function, skin differentiation, and reproduction, as well as vascular and metabolic properties. From observational studies in human subjects, poor vitamin D status is associated with nearly all diseases predicted by these extraskeletal actions. Results of randomized controlled trials and Mendelian randomization studies are supportive of vitamin D supplementation in reducing the incidence of some diseases, but, globally, conclusions are mixed. These findings point to a need for continued ongoing and future basic and clinical studies to better define whether vitamin D status can be optimized to improve many aspects of human health. Vitamin D deficiency enhances the risk of osteoporotic fractures and is associated with many diseases. We review what is established and what is plausible regarding the health effects of vitamin D.

[Rickets/Osteomalacia. Non-skeletal effects of vitamin D.]

A variety of epidemiological studies and meta-analyses have shown that vitamin D insufficiency or deficiency not only affects bone and mineral metabolism, but is also linked to sarcopenia, metabolic diseases such as diabetes, obesity, and metabolic syndrome, cancer, autoimmune disease, and other diseases. There has been accumulating evidence that vitamin D deficiency, defined as a serum 25(OH)D value below 20 ng/mL, is a significant risk factor for each of these diseases. However, vitamin D supplementation has not shown a therapeutic effect in any of these diseases, and a detailed cause-and-effect relationship remains elusive. Future studies should consider non-skeletal effects when investigating cutoff levels of serum 25(OH)D for therapeutic intervention in vitamin D insufficiency and deficiency, the required supplement dose, and the length of supplementation.

[Rickets/Osteomalacia. Symptomatic vitamin D deficiency in children and its prevention and treatment.]

Vitamin D deficiency rickets is characterized by mineralization impairment in bone and cartilage of children caused by vitamin D deficiency in the body due to limited sunlight exposure and vitamin D intake. Vitamin D supplementation is recommended in developed countries. Low calcium intake is a risk factor for vitamin D deficiency rickets. For treatment, native vitamin D is used in developed countries, while active vitamin D is used in Japan.

[Rickets and anaemia caused by coeliac disease in a three-year-old girl].

We present a case report of a three-year-old girl of Pakistani origin with coeliac disease. The first symptom was spontaneous fracture of the fibula. Vitamin D deficiency rickets and iron deficiency anaemia were demonstrated. An intestinal biopsy and elevated antibody levels confirmed the coeliac disease. Rickets is a known but rare presentation of coeliac disease, but this case report illustrates, how coeliac disease in children often presents with non-gastrointestinal symptoms. The importance of investigations for malabsorp-tion, if iron deficiency is not easily corrected with sufficient iron supplements, is underlined as well as the importance of screening for coeliac disease.

Health Risks of Hypovitaminosis D: A Review of New Molecular Insights.

Hypovitaminosis D has become a pandemic, being observed in all ethnicities and age groups worldwide. Environmental factors, such as increased air pollution and reduced ultraviolet B (UVB) irradiation, as well as lifestyle factors, i.e., decreased outdoor activities and/or poor intake of vitamin D-rich food, are likely involved in the etiology of a dramatic reduction of vitamin D circulating levels. The insufficiency/deficiency of vitamin D has long been known for its association with osteoporosis and rickets. However, in the last few decades it has become a serious public health concern since it has been shown to be independently associated with various chronic pathological conditions such as cancer, coronary heart disease, neurological diseases, type II diabetes, autoimmune diseases, depression, with various inflammatory disorders, and with increased risk for all-cause mortality in the general population. Prevention strategies for these disorders have recently involved supplementation with either vitamin D2 or vitamin D3 or their analogs at required daily doses and tolerable upper-limit levels. This review will focus on the emerging evidence about non-classical biological functions of vitamin D in various disorders.

Cortical Matrix Mineral Density Measured Noninvasively in Pre- and Postmenopausal Women and a Woman With Vitamin D-Dependent Rickets.

Reduced bone mineral density (BMD) may be due to reduced mineralized bone matrix volume, incomplete secondary mineralization, or reduced primary mineralization. Because bone biopsy is invasive, we hypothesized that noninvasive image acquisition at high resolution can accurately quantify matrix mineral density (MMD). Quantification of MMD was confined to voxels attenuation photons above 80% of that produced by fully mineralized bone matrix because attenuation at this level is due to variation in mineralization, not porosity. To assess accuracy, 9 cadaveric distal radii were imaged at a voxel size of 82 microns using high-resolution peripheral quantitative computed tomography (HR-pQCT; XtremeCT, Scanco Medical AG, Bruttisellen, Switzerland) and compared with VivaCT 40 (µCT) at 19-micron voxel size. Associations between MMD and porosity were studied in 94 healthy vitamin D-replete premenopausal women, 77 postmenopausal women, and in a 27-year-old woman with vitamin D-dependent rickets (VDDR). Microstructure and MMD were quantified using StrAx (StraxCorp, Melbourne, Australia). MMD measured by HR-pQCT and µCT correlated (R = 0.87; p < 0.0001). The precision error for MMD was 2.43%. Cortical porosity and MMD were associated with age (r2 = 0.5 and -0.4, respectively) and correlated inversely in pre- and postmenopausal women (both r2 = 0.9, all p < 0.001). Porosity was higher, and MMD was lower, in post- than in premenopausal women (porosity 40.3% ± 7.0 versus 34.7% ± 3.5, respectively; MMD 65.4% ± 1.8 versus 66.6% ± 1.4, respectively, both p < 0.001). In the woman with VDDR, MMD was 5.6 SD lower and porosity was 5.6 SD higher than the respective trait means in premenopausal women. BMD was reduced (Z-scores femoral neck -4.3 SD, lumbar spine -3.8 SD). Low-radiation HR-pQCT may facilitate noninvasive quantification of bone's MMD and microstructure in health, disease, and during treatment. © 2018 American Society for Bone and Mineral Research.

Iron Supplementation Associated With Loss of Phenotype in Autosomal Dominant Hypophosphatemic Rickets.

CONTEXT: Autosomal dominant hypophosphatemic rickets (ADHR) is the only hereditary disorder of renal phosphate wasting in which patients may regain the ability to conserve phosphate. Low iron status plays a role in the pathophysiology of ADHR. OBJECTIVE: This study reports of a girl with ADHR, iron deficiency, and a paternal history of hypophosphatemic rickets that resolved without treatment. The girl's biochemical phenotype resolved with iron supplementation. SUBJECTS: A 26-month-old girl presented with typical features of hypophosphatemic rickets, short stature (79 cm; -2.82 SDS), and iron deficiency. Treatment with elemental phosphorus and calcitriol improved her biochemical profile and resolved the rickets. The girl's father had presented with rickets at age 11 months but never received medication. His final height was reduced (154.3 cm; -3.51 SDS), he had undergone corrective leg surgery and had an adult normal phosphate, fibroblast growth factor 23, and iron status. Father and daughter were found to have a heterozygous mutation in exon 3 of the FGF23 gene (c.536G>A, p.Arg179Gln), confirming ADHR. INTERVENTION: Withdrawal of rickets medication was attempted off and on iron supplementation. RESULTS: Withdrawal of rickets medication in the girl was unsuccessful in the presence of low-normal serum iron levels at age 5.6 years but was later successful in the presence of high-normal serum iron levels following high-dose iron supplementation. CONCLUSIONS: We report an association between iron supplementation and a complete loss of biochemical ADHR phenotype, allowing withdrawal of rickets medication. Experience from this case suggests that reduction and withdrawal of rickets medication should be attempted only after iron status has been optimized.