Rickets

Rickets is the pediatric skeletal disease that results when vitamin D and/or dietary calcium supply is inadequate to meet the mineral demands of a growing skeleton — a disorder of defective growth-plate chondrocyte differentiation and apoptosis, and defective mineralization of newly formed bone matrix (osteoid), caused by vitamin D deficiency and/or low calcium intake in children.^[1] Its adult, post-growth-plate-fusion equivalent, osteomalacia (defective mineralization of already-formed bone), shares the same underlying biochemistry but produces a different clinical picture and is outside this chapter's primary scope.^[1]

Nutritional vitamin D-deficiency rickets — from inadequate vitamin D intake and/or synthesis, often compounded by low dietary calcium — is overwhelmingly the dominant cause worldwide, and remains a genuinely persistent, largely preventable problem in Canada despite decades of public health guidance.^[1][2] A national Canadian Paediatric Surveillance Program study identified 104 confirmed cases of vitamin D-deficiency rickets in Canadian children over a two-year active-surveillance period, an overall annual incidence of roughly 2.9 per 100,000, with the highest rates among children living in the North (Yukon, Northwest Territories, and Nunavut) and among infants with darker skin pigmentation who were breastfed without vitamin D supplementation — and, tellingly, no cases occurred among breastfed infants who had actually received the recommended 400 IU/day of vitamin D from birth, meaning the guidance genuinely works when it is actually followed; the persistent disease burden reflects a real-world implementation gap, not a gap in the evidence.^[3] This is a genuinely high-value pharmacist counseling opportunity: parents deciding whether to buy, and then consistently give, an infant vitamin D supplement are making exactly the decision this data is about.

This chapter covers nutritional vitamin D-deficiency rickets in depth — its classic skeletal findings, radiographic confirmation, biochemical diagnosis, the Canadian Paediatric Society's infant and pregnancy supplementation recommendations for prevention, and the age-based treatment regimen for confirmed disease — together with a concise, clinically practical overview of the hereditary and refractory forms that mimic it but do not respond to standard vitamin D dosing: X-linked hypophosphatemic rickets (XLH) and vitamin D-dependent rickets (VDDR) types 1 and 2.^[4][5]

Skeletal (osseous) findings

The clinical picture reflects impaired mineralization at the sites of most active bone growth, and its exact appearance depends heavily on the child's age and stage of growth.^[1] Craniotabes — softening of the skull bones, felt as a springy, ping-pong-ball-like give on gentle palpation of the parietal or occipital bones — is usually evident in the first 3 months of life, before weight-bearing findings appear.^[1] Delayed fontanelle closure (normally closed by 2 years) and frontal bossing are also early findings.^[1] As teeth and ribs develop, delayed tooth eruption (no incisors by 10 months, no molars by 18 months) and the rachitic rosary — palpable, sometimes visible enlargement of the costochondral junctions, felt anteriorly along the lateral chest wall — become apparent.^[1] Once a child begins bearing weight, leg deformity becomes the most recognizable feature: genu varum (bowed legs) is the classic presentation in toddlers, though genu valgum (knock-knees) or a mixed "windswept" deformity (one leg varus, the other valgus) also occur.^[1] Swelling of the wrists and ankles, from the widened, under-mineralized metaphyses, is often palpable. Longstanding disease can progress to pelvic deformity, including outlet narrowing that carries a genuine risk of obstructed labor and maternal/fetal death if it persists into a female patient's own future pregnancies — a rare but devastating long-term consequence worth knowing about even though its relevance is decades removed from an initial pediatric diagnosis.^[1] Bone pain, restlessness, and irritability are common and may be the presenting complaint before deformity is obviously visible.^[1]

Non-osseous and systemic findings

Rickets is not only a bone disease. Failure to thrive and poor linear growth are common.^[1] Delayed gross motor development with muscle weakness — a waddling gait, difficulty climbing stairs, reluctance to bear weight — reflects the myopathy that frequently accompanies vitamin D deficiency, not only the skeletal changes.^[1] More acutely and more dangerously, hypocalcemia (see Assessment & Diagnosis) can produce seizures and tetanic spasms, and — rarely, but genuinely reported even in developed countries — hypocalcemic dilated cardiomyopathy with heart failure, arrhythmia, or cardiac arrest.^[1] A hypocalcemic seizure in an otherwise well-appearing young infant, especially one who is exclusively breastfed without vitamin D supplementation, should prompt consideration of underlying rickets even before overt skeletal findings are present — see Risk Factors and Red Flags & Refer.^[3] Raised intracranial pressure is a rare but reported association.^[1]

A wrist radiograph showing the classic metaphyseal "cupping" of rickets — the widened, frayed, poorly mineralized growth plate that confirms the diagnosis radiographically. (Frank Gaillard, CC BY-SA 4.0, Wikimedia Commons)

The radiographic hallmark

Radiographs of the wrist and/or knee — the sites of fastest linear growth, and therefore the most active, most visibly affected growth plates — confirm the diagnosis once clinical and biochemical findings raise suspicion.^[1][4] Classic findings are splaying, fraying, and cupping of the metaphyses with a coarse trabecular pattern, widening of the growth plate, generalized osteopenia, and, in more advanced disease, pelvic deformity or a minimal-trauma fracture.^[1] Radiographically confirmed rickets carries a measurably increased fracture risk; simple biochemical vitamin D deficiency without radiographic rickets does not appear to carry the same increased risk.^[1]

Maternal factors (during pregnancy)

• Maternal vitamin D deficiency — from dark skin pigmentation, full-body clothing cover, high latitude during winter/spring, predominantly indoor living, disability limiting outdoor time, air pollution or heavy cloud cover, a low-vitamin-D diet, or poverty/malnutrition/restrictive diets — is the single most consistent upstream driver of neonatal and early infantile rickets, since a deficient mother cannot pass adequate vitamin D stores to her infant in utero or through breast milk.^[1]
• Low maternal dietary calcium intake compounds the risk independent of vitamin D status.^[1]

Infant and childhood factors

• Exclusive or prolonged breastfeeding without vitamin D supplementation is the dominant, most consistently reported risk factor for infantile rickets in both the published literature and Canadian surveillance data.^[1][3] This is not a reason to avoid or limit breastfeeding — human breast milk is intrinsically very low in vitamin D regardless of maternal diet, so the fix is supplementing the infant, not changing how the infant is fed; see Non-Pharmacologic Treatment.
• Prolonged breastfeeding with late introduction of complementary feeding (after 6 months) that does not include calcium-rich foods.^[1]
• Dark skin pigmentation — melanin competes with 7-dehydrocholesterol for the same UVB photons, so more heavily pigmented skin requires substantially longer sun exposure to synthesize an equivalent amount of previtamin D3 — combined with restricted UVB exposure from predominantly indoor living, disability, air pollution, or heavy cloud cover.^[1]
• High latitude, particularly during winter and spring — genuinely Canada-relevant, since most of the Canadian population lives at a latitude where the UVB wavelengths needed for cutaneous vitamin D synthesis are weak or absent for several winter months regardless of time spent outdoors, and risk rises further the farther north a family lives.^[1][2]
• A low-vitamin-D or low-calcium diet, including exclusively plant-based milk alternatives (soy, almond, oat, rice) used in place of breast milk, standard infant formula, or cow's milk without confirming they are fortified and nutritionally appropriate for the child's age.
• Poverty, malnutrition, and restrictive diets, including some vegan, macrobiotic, or rice-based diets without adequate fortified substitutes.^[1]

Also refer for:

• Any child with clinical and/or radiographic findings suggestive of rickets, for confirmatory biochemistry and radiographs and to establish a treatment plan — this is not a condition to manage on clinical impression alone.
• Suspected non-nutritional (hereditary or secondary) rickets: presentation in early infancy before major nutritional/sun-exposure risk factors are plausible, disproportionate hypophosphatemia with normal or only mildly elevated PTH and normal calcium, a markedly elevated rather than low 1,25-dihydroxyvitamin D, a positive family history, or alopecia in a child with rachitic features — see Assessment & Diagnosis for the full differentiating pattern and Choose Initial Treatment for why these will not respond to standard vitamin D dosing.
• Failure to respond adequately — clinically, biochemically, or radiographically — after a confirmed-adherent, correctly dosed 3-month course of treatment for presumed nutritional rickets; see Treatment Failure / Next Step.
• Rickets in a child with known malabsorption (fat malabsorption, celiac disease, cystic fibrosis, hepatobiliary disease), chronic kidney disease, or long-term anticonvulsant therapy — these need condition-specific specialist management rather than the standard nutritional-rickets protocol.
• Significant or worsening leg deformity, for orthopedic assessment alongside medical treatment.
• A newly confirmed hereditary rickets diagnosis, for genetic counselling given the family-planning implications.

How the diagnosis is made

Rickets is diagnosed on the basis of history, physical examination, and biochemical testing, and confirmed by radiographs; biochemical testing alone is not sufficient to diagnose rickets or to determine whether vitamin D deficiency, dietary calcium deficiency, or both are the primary driver, because combined deficiencies are common.^[1]

Vitamin D status — serum 25-hydroxyvitamin D (25OHD)

A 25OHD level below roughly 34 nmol/L is associated with a rising PTH in most reported series, which is why 25OHD in the 30-34 nmol/L range is considered the approximate threshold below which rickets becomes more likely — though rickets has been reported at higher 25OHD levels when dietary calcium intake is also low, underscoring that vitamin D and calcium status interact rather than acting as two fully independent risk factors.^[1]

The full biochemical pattern in nutritional rickets

Typical findings are decreases in 25OHD, serum phosphorus, serum calcium, and urinary calcium, with serum PTH, alkaline phosphatase (ALP), and urinary phosphorus invariably elevated — the elevated PTH is a secondary hyperparathyroidism response to hypocalcemia, and it is this PTH elevation, not the vitamin D deficiency directly, that drives the phosphate wasting and resulting impaired mineralization.^[1]

Dietary calcium intake, by age

Recognizing when it is not nutritional rickets

The pattern above assumes ordinary nutritional vitamin D and/or calcium deficiency. A small but clinically important minority of rachitic children have a hereditary cause that will not respond to standard vitamin D dosing (see Choose Initial Treatment) and needs specialist-directed therapy instead. The pattern of calcium, phosphate, PTH, 25OHD, and 1,25-dihydroxyvitamin D (the activated hormone) is usually enough to tell these apart:^[4][5]

See Choose Initial Treatment for what each of these patterns means for treatment, and Red Flags & Refer for when to send a child for this workup rather than continuing standard nutritional dosing.

• Achieve full biochemical and radiographic healing — normalization of serum calcium, phosphate, and alkaline phosphatase, and resolution of the metaphyseal changes on repeat imaging — not merely resolution of symptoms.^[1]
• Restore and then maintain serum 25-hydroxyvitamin D above the sufficiency threshold of 50 nmol/L.^[1]
• Ensure adequate concurrent elemental calcium intake throughout treatment — combined calcium-plus-vitamin-D therapy heals nutritional rickets faster and more completely than either given alone, since the underlying deficiency is very often mixed rather than purely vitamin D.^[1]
• Avoid vitamin D toxicity — hypercalcemia and hypercalciuria from a 25OHD level above 250 nmol/L — particularly with single large "stoss" doses, which require correct age-based dosing rather than an extrapolated or rounded-up dose.^[1]
• Prevent the complications of untreated or under-treated disease across every affected domain: fracture, permanent skeletal deformity, growth delay, and the acute hypocalcemic seizure/cardiomyopathy risk described in Red Flags & Refer.
• At the population level, achieve universal, correctly dosed infant vitamin D supplementation from birth — Canadian surveillance data shows this genuinely prevents the disease; the treatment gap is overwhelmingly an implementation gap, not a knowledge gap.^[3]
• Recognize non-response early — reassess at 3 months rather than continuing to escalate nutritional dosing indefinitely — so a hereditary or refractory cause is not missed and specialist-directed therapy is not delayed.^[1]

What does not work — and how to recognize it early

If the biochemical pattern points toward a hereditary or refractory cause (see the differential table in Assessment & Diagnosis), standard vitamin D3/D2 dosing, at any dose, will not correct it, because the defect lies downstream of, or is unrelated to, ordinary vitamin D substrate supply. These children need specialist-directed therapy:

Sun exposure — a genuine but genuinely limited tool

UVB radiation triggers epidermal synthesis of previtamin D3, and restricted sun exposure is a real contributor to nutritional rickets risk.^[1] But latitude, season, time of day, cloud cover, pollution, skin coverage, and skin pigmentation all affect how much UVB actually reaches the skin and how efficiently it is converted — and, critically, no safe threshold of UV exposure exists that reliably provides sufficient vitamin D synthesis without also increasing skin cancer risk.^[1] Do not recommend increased unprotected sun exposure, including sunlight through a window (glass filters out the effective UVB wavelengths), as a rickets prevention or treatment strategy in place of dietary intake and supplementation — this applies with particular force in Canada, where winter UVB is minimal or absent at most latitudes regardless of time spent outdoors.

Continue breastfeeding — supplement the infant, don't stop feeding

A rickets diagnosis, or a parent's worry about it, is not a reason to stop or limit breastfeeding. Human breast milk is intrinsically very low in vitamin D regardless of maternal diet or how well-nourished the mother is, so the actual fix is giving the infant a vitamin D supplement (and correcting maternal vitamin D deficiency, if present) — not weaning or switching to formula. This reassurance is worth stating explicitly and proactively, since "stop breastfeeding" is an intuitive but incorrect response that some parents may otherwise reach for on their own.

Complementary feeding and food sources

• Introduce complementary foods no later than 26 weeks (6 months) of age, including sources rich in calcium.^[1]
• Ensure at least 500 mg/day of elemental calcium intake through childhood and adolescence, through diet, fortified foods, or supplementation.^[1]
• In Canada, cow's milk and margarine are mandatorily fortified with vitamin D, and standard infant formula is fortified as well — but plant-based milk alternatives (soy, almond, oat, rice) are not nutritionally interchangeable with cow's milk or infant formula for a young child, and families using them in place of dairy or formula should be specifically asked whether the product is fortified and age-appropriate.

Adherence support — a genuinely practical pharmacist role

• Counsel on accurate dropper technique for liquid infant vitamin D products — under- or over-filling the dropper is a common, easily correctable source of under- or over-dosing.
• Distinguish clearly, when dispensing, between routine daily prevention-dose products and any prescription high-dose treatment or stoss-therapy product a specialist has prescribed — these should never be conflated or substituted for one another at the counter.
• Build consistent daily administration into an existing routine (e.g., with a feed) to support the full 12-week treatment course, not just the first few weeks.

Orthopedic input and genetic counselling

• Most bowing in a young child corrects with medical healing alone once the underlying deficiency is treated; bracing or surgery is reserved for older children with residual deformity that persists after adequate biochemical healing has been achieved and confirmed.
• Offer genetic counselling for any confirmed hereditary rickets diagnosis (XLH is X-linked dominant; VDDR is autosomal recessive), given the clear inheritance pattern and family-planning implications.^[4][5]

Lactation and the breastfed infant

Maternal supplementation during breastfeeding meets the mother's own vitamin D requirement, but does not reliably supply the infant's — maternal vitamin D and calcium intake during lactation is not associated with meaningfully different breast milk vitamin D content, so a lactating mother should not rely on her own supplementation as a substitute for directly supplementing her infant.^[1] Every breastfed or partially breastfed infant needs their own vitamin D supplement from birth; see Choose Initial Treatment and Non-Pharmacologic Treatment.

Indigenous, northern, and dark-skinned infant populations

The Canadian Paediatric Society specifically names Indigenous infants and children, along with other infants at elevated risk (dark skin pigmentation, limited sun exposure, northern latitude, or a vitamin-D-deficient mother), as warranting the higher 800 IU/day supplementation dose in the first year of life, rather than the standard 400 IU/day.^[2] This reflects both the documented elevated disease burden in these populations in Canadian surveillance data and the CPS's explicit aim of preventing symptomatic disease before it occurs, not just treating it once it appears.^[2][3] For high-risk families with genuine adherence difficulty, specialist consultation about an intermittent, higher-dose oral vitamin D regimen is a reasonable option.^[2]

Formula-fed infants

Standard infant formula is fortified with vitamin D; a formula-fed infant taking at least 800-1,000 mL/day of formula does not need additional supplementation at low risk, but an infant at high risk, or one not yet reliably consuming that volume, should still receive 400 IU/day.^[2]

Children 1-5 years

Low-risk children need only ongoing dietary guidance to meet vitamin D needs through fortified foods; high-risk children should continue 400 IU/day of supplementation alongside dietary guidance.^[2]

Preterm and very-low-birth-weight infants

Rickets and bone disease in preterm infants ("osteopenia of prematurity") reflects a different, primarily mineral-accretion-driven mechanism rather than simple vitamin D deficiency, and needs neonatology-directed, weight-based mineral supplementation protocols that are outside this chapter's scope — refer rather than applying the term-infant dosing above.

Malabsorption, hepatic, renal, and anticonvulsant-related rickets

Children with fat malabsorption (celiac disease, cystic fibrosis), hepatobiliary disease, chronic kidney disease, or long-term enzyme-inducing anticonvulsant therapy are at risk of vitamin D deficiency or altered vitamin D metabolism through mechanisms distinct from simple dietary/sun-exposure deficiency, and often need higher, condition-specific dosing or an active vitamin D metabolite directed by the relevant specialist rather than the standard nutritional-rickets regimen.^[1]

During and after standard nutritional-rickets treatment

Reassess clinically and biochemically at the end of the 3-month (12-week) treatment course — repeat serum calcium, phosphate, alkaline phosphatase, PTH, and 25OHD, and repeat the wrist and/or knee radiograph if it was initially abnormal or if healing is in doubt.^[1] Some children need a longer treatment course to achieve full biochemical and radiographic healing.^[1] Once treatment is complete, transition to the age-appropriate maintenance dose (400 IU/day under 12 months, 600 IU/day from 12 months) indefinitely, rather than stopping supplementation altogether.^[1] Track growth parameters at routine well-child visits.

Watch for over-treatment, not just under-treatment

High-dose repletion and stoss-therapy regimens carry a real, if uncommon, risk of vitamin D toxicity — hypercalcemia and hypercalciuria from a 25OHD level above 250 nmol/L.^[1] This risk rises specifically when families layer additional over-the-counter vitamin D products on top of a prescribed high-dose regimen without telling the care team — ask about this explicitly rather than assuming it isn't happening.

Hereditary and refractory forms — specialist-directed follow-up

Children with XLH need structured, more frequent specialist follow-up: visits as often as monthly to 3-monthly in the first 5 years of life, tapering to every 6-12 months in adulthood, with growth parameters, musculoskeletal function, and orthopedic, dental (twice yearly), and hearing assessment (from age 8) at each stage, alongside serum ALP/calcium/phosphate/PTH/25OHD and a urinary calcium/creatinine ratio.^[4] Children on burosumab need additional, closer fasting-phosphate monitoring — every 2 weeks during the first month of treatment, then every 4 weeks for the following 2 months, and again 4 weeks after any dose adjustment — to detect both hyperphosphatemia (withhold the dose) and underdosing (restart at roughly half the previous dose once phosphate has normalized below range).^[4] VDDR2A specifically benefits from continued follow-up through puberty, since calcium absorption often improves afterward and supplementation needs can decrease substantially.^[5]

1. Confirm actual adherence and correct administration before concluding treatment has failed — inaccurate liquid-dropper dosing in infants is a common, easily corrected cause of apparent non-response.
2. Confirm the correct age-based dose and the full minimum 12-week duration were actually used; a too-low dose, or a course stopped early before reassessment, is not a true treatment failure.
3. Reassess dietary calcium intake specifically — inadequate concurrent calcium intake can blunt or delay biochemical and radiographic healing even when vitamin D repletion itself has been adequate and correctly dosed.
4. Screen for malabsorption (fat malabsorption, celiac disease, cystic fibrosis, hepatobiliary disease) if there are coexisting GI symptoms, poor growth, or other reasons to suspect reduced oral absorption of vitamin D or calcium.
5. If adherence, dosing, duration, and dietary calcium are all genuinely adequate and the biochemical/radiographic response at 3 months is still inadequate, refer to pediatric endocrinology for a hereditary or refractory rickets workup (PHEX/FGF23 testing for XLH; CYP27B1 or VDR analysis for VDDR) rather than simply repeating or escalating the standard nutritional regimen further.
6. Recognize the biochemical red flags that should prompt earlier referral rather than waiting the full 3 months: disproportionate hypophosphatemia with a normal or only mildly elevated PTH and normal calcium (suggests XLH); a markedly elevated rather than low 1,25-dihydroxyvitamin D (suggests VDDR2A); onset with hypocalcemic symptoms in the first two years of life with a normal or increased 25OHD (suggests VDDR1A); or alopecia in a rachitic child (a genuinely specific clue for VDDR2A).

• Treating a child whose biochemical pattern actually fits a hereditary cause (disproportionate hypophosphatemia with normal/low PTH and normal calcium, or a markedly elevated rather than low 1,25-dihydroxyvitamin D) with standard vitamin D dosing — it will not work, and delays the specialist-directed therapy these children actually need.
• Recommending increased unprotected sun exposure, including sunlight through a window, as a rickets prevention or treatment strategy — no safe UV threshold exists that avoids raising skin cancer risk, and window glass filters out the effective wavelengths anyway.
• Advising a breastfeeding mother to stop or limit breastfeeding because of a rickets diagnosis — the actual fix is infant vitamin D supplementation (and maternal repletion if the mother is also deficient), not weaning.
• Prescribing or recommending an active vitamin D analogue (calcitriol or alfacalcidol) for ordinary nutritional vitamin D-deficiency rickets — unnecessary and more expensive, since the problem there is substrate supply, not the renal activation step these analogues bypass.
• Giving phosphate salts for XLH without a co-administered active vitamin D analogue, which risks worsening secondary hyperparathyroidism.
• Combining burosumab with conventional phosphate/active-vitamin-D therapy, or starting burosumab when fasting phosphate is already within the age-related normal range.
• Assuming mild leg bowing in a young toddler needs urgent orthopedic bracing or surgery before a metabolic workup and an adequate medical treatment trial — most corrects with medical healing alone.
• Missing a hypocalcemic seizure as a presentation of rickets in a young, exclusively breastfed, unsupplemented infant — especially in populations named at elevated risk by Canadian guidance.
• Assuming formula feeding alone guarantees adequate vitamin D intake before the infant is reliably taking the 800-1,000 mL/day threshold that actually provides it.
• Treating an infant's rickets without also asking about and addressing maternal vitamin D status during the pregnancy and any ongoing breastfeeding, when maternal deficiency is a plausible contributor.

How to use this table: Doses are pediatric doses and require patient-specific confirmation (weight, renal function, adherence to a co-therapy). Select any linked drug name to open its complete Pharmasist Drug Database page. Ergocalciferol (vitamin D2), calcium citrate, and calcifediol do not currently have their own published Drug Database entries, so each is named as text only where it appears below rather than linked — see the chapter note at the top of this source file for the full explanation.

Nutritional vitamin D-deficiency rickets — first-line therapy

Oral vitamin D dosed by age for a minimum 12-week course, always combined with elemental calcium regardless of the child's age or weight.

Vitamin D-dependent rickets type 1A — active vitamin D replacement

For confirmed CYP27B1-deficiency rickets, which does not respond to vitamin D3/D2 at any dose because the enzyme that activates it is missing.

Vitamin D-dependent rickets type 2A — high-dose calcium is the primary lever

For confirmed vitamin D receptor (VDR) resistance. Because the defect is receptor-level, even very high-dose calcitriol often cannot fully overcome it — high-dose calcium, not vitamin D dosing, does most of the work here.

X-linked hypophosphatemic rickets — conventional therapy

Combination oral phosphate salts plus an active vitamin D analogue, started as soon as the diagnosis is established in a child with an overt XLH phenotype.

X-linked hypophosphatemic rickets — targeted anti-FGF23 therapy

For children aged 1 year or older (and adolescents with a growing skeleton) with radiographic evidence of overt bone disease who are refractory to, experiencing complications from, or unable to adhere to conventional therapy. Never combine with conventional phosphate/active vitamin D therapy — stop conventional therapy before starting.

Secondary hyperparathyroidism and acute hypocalcemia — adjuncts

Reserve for the specific situations named below rather than as routine therapy.