The authors have declared that no competing interests exist.
Conceived and designed the experiments: RJB JOW CJG SOS ARM. Performed the experiments: STG SP. Analyzed the data: STG RH JCK. Contributed reagents/materials/analysis tools: JS SR CY. Contributed to the writing of the paper: CG AM SR CY SP JK JS RLH SS JW. Wrote the paper: STG RB.
Observational studies suggest high prenatal vitamin D intake may be associated with reduced childhood wheezing. We examined the effect of prenatal vitamin D on childhood wheezing in an interventional study.
We randomised 180 pregnant women at 27 weeks gestation to either no vitamin D, 800 IU ergocalciferol daily until delivery or single oral bolus of 200,000 IU cholecalciferol, in an ethnically stratified, randomised controlled trial. Supplementation improved but did not optimise vitamin D status. Researchers blind to allocation assessed offspring at 3 years. Primary outcome was any history of wheeze assessed by validated questionnaire. Secondary outcomes included atopy, respiratory infection, impulse oscillometry and exhaled nitric oxide. Primary analyses used logistic and linear regression.
We evaluated 158 of 180 (88%) offspring at age 3 years for the primary outcome. Atopy was assessed by skin test for 95 children (53%), serum IgE for 86 (48%), exhaled nitric oxide for 62 (34%) and impulse oscillometry of acceptable quality for 51 (28%). We found no difference between supplemented and control groups in risk of wheeze [no vitamin D: 14/50 (28%); any vitamin D: 26/108 (24%) (risk ratio 0.86; 95% confidence interval 0.49, 1.50; P = 0.69)]. There was no significant difference in atopy, eczema risk, lung function or exhaled nitric oxide between supplemented groups and controls.
Prenatal vitamin D supplementation in late pregnancy that had a modest effect on cord blood vitamin D level, was not associated with decreased wheezing in offspring at age three years.
Controlled-Trials.com
Several observational studies have suggested a protective effect of higher maternal vitamin D intake during pregnancy on risk of wheezing
There are plausible biological mechanisms for an association between prenatal 25(OH)D status and wheezing. Developmental programming of lung function and immune responses occurs during pregnancy
The protocol for this trial and supporting CONSORT checklist are available as supporting information; see
St. Mary’s Hospital Research Ethics Committee approved the follow up study (10/H0712/13) and women gave written informed consent to participation for themselves and their child. Where women only consented to interview over the telephone, verbal consent was taken in place of written consent and this was approved by the Ethics Committee. For each participant who gave verbal consent, this was taken and documented by 2 separate members of the research team.
This was a prospective follow up study of the offspring of women who took part in an ethnically stratified, parallel group, randomised controlled trial of vitamin D supplementation in pregnancy at St Mary’s Hospital London, a university-affiliated hospital prenatal clinic, between April and November 2007. The original trial was conducted to determine the effect of supplementation on 25(OH)D status of mothers in 4 specific ethnic groups, and their babies, at delivery
Women were randomised at 27 weeks gestation to no treatment (control), 800 IU ergocalciferol until delivery (daily), or a single oral dose of 200,000 IU cholecalciferol (bolus). The randomisation sequence was generated by an independent researcher using computer generated random number lists in blocks of 15, stratified by 4 ethnic groups in a 1∶1:1 ratio. The researcher gave participants a study number on entry to the trial, and treatment was allocated from the hospital pharmacy. Women were given instructions to swallow the tablets whole and to avoid other multivitamin supplements containing vitamin D. This trial was conducted before national guidance on routinely providing advice on vitamin D intake during pregnancy was introduced in March 2008
The primary outcome was prevalence of ‘wheeze ever’ as defined by the International Study of Asthma and Allergies in Childhood (ISAAC)
Exhaled nitric oxide (eNO) was measured using an offline, tidal breathing technique adherent to ATS/ERS guidelines
Allergic sensitisation was defined as a skin prick test wheal at least 3 mm greater than the negative control (Glycerine) to one or more of the aeroallergens tested at 15 minutes, in the context of an appropriate response to the positive control (Histamine 10%). House dust mite, alternaria, cladosporium, cat, dog, grass pollen, silver birch pollen, peanut, milk and egg were tested (Stallergenes, Antony, France).
Serum total IgE (ImmunoCAP, Phadia, Uppsala, Sweden), 25(OH)D and eosinophil count were determined on the day of the child’s assessment. 25(OH)D was measured in mothers prior to randomisation, and in offspring at birth (cord blood) using a radio-immunoassay (DiaSorin, Stilwater, MN) in a clinical biochemistry laboratory that participates in the international Vitamin D external quality assessment program (DEQAS). Vitamin D deficiency was defined as 25(OH)D <25 nmol/L
Primary health care records were obtained from participants’ general practitioners and reviewed by a single investigator (RJB), blinded to treatment allocation. Children were categorised as having ‘recurrent wheezing’ where ≥2 episodes of either wheezing, or respiratory distress treated with bronchodilator were recorded; ‘eczema’ if they had ≥2 attendances separated by ≥6 months where either topical corticosteroids were prescribed for treatment of an itchy skin rash, or a doctor’s diagnosis of eczema was made; and ‘food allergy’ if this diagnosis was recorded in any part of the primary healthcare record.
In the original study it was calculated that at least eight women in each ethnic group for each arm of treatment would be needed to demonstrate a significant difference in vitamin D levels at delivery in the no treatment group vs. the supplemented groups (power 90%, test of significance at 5% level). To account for drop-outs, preterm delivery, and delivery at another hospital, 15 women were allocated to each arm of treatment within each ethnic group (n = 180).
With 180 participants and 80% successful follow up, this study had 80% power with 2-sided alpha of 0.05 to detect a reduction in wheeze from 34% in the children of non-supplemented mothers
Adjustment for multiple testing was performed using the Benjamini and Hochberg method
Participant flow is shown in
Control | Daily vitamin D | Bolus vitamin D | Combined vitamin D | |
(n = 50) | (n = 56) | (n = 52) | (n = 108) | |
Baseline maternal 25(OH)D <25 nmol/L, n/N (%) | 24/50 (48) | 25/56 (45) | 22/52 (42) | 47/108 (44) |
Male sex, n/N (%) | 27/50 (54) | 32/56 (57) | 26/52 (50) | 58/108 (55) |
Birth weight (g), mean (SD) | 3268 (585) | 3321 (525) | 3290 (467) | 3307 (497) |
Ethnicity, n (%) | ||||
Asian | 12 (24) | 15 (27) | 13 (25) | 28 (26) |
Middle Eastern | 13 (26) | 14 (25) | 14 (26) | 28 (26) |
Black | 12 (24) | 14 (25) | 13 (25) | 27 (25) |
White | 13 (26) | 13 (23) | 12 (24) | 25 (23) |
GA at delivery (weeks), mean (SD) | 40 (1) | 39 (2) | 40 (1) | 39 (2) |
Nulliparous mother, n/N (%) | 23/50 (46) | 20/56 (36) | 21/52 (40) | 41/108 (38) |
Vaginal delivery, n/N (%) | 29/50 (58) | 35/56 (63) | 28/52 (54) | 63/108 (58) |
Maternal smoking during pregnancy, n/N (%) | 2/48 (4) | 3/55 (5) | 0/46 (0) | 3/101 (3) |
Presence of household smokers, n/N (%) | 16/48 (33) | 15/55 (27) | 17/46 (37) | 32/101 (32) |
Number of children in household, mean (SD) | 2 (1) | 2 (1) | 2 (1) | 2 (1) |
Age mother left full time education, mean (SD) | 20 (3) | 20 (4) | 21 (4) | 21 (4) |
Child in nursery, n/N (%) | 27/48 (56) | 36/55 (65) | 20/45 (44) | 57/101 (56) |
Cat or dog in household, n/N (%) | 4/48 (8) | 5/54 (9) | 4/46 (9) | 9/100 (9) |
Maternal Fitzpatrick skin score grade 3–6, n/N (%) | 28/44 (64) | 33/49 (67) | 28/43 (65) | 61/92 (66) |
Maternal regular vitamin intake at three years, n/N (%) | 9/46 (20) | 16/53 (30) | 16/45 (36) | 32/98 (33) |
At least one parent with allergic disease, n/N (%) | 23/45 (51) | 35/53 (66) | 21/45 (47) | 56/98 (57) |
Exclusively breast-fed for 4 months, n/N (%) | 22/48 (46) | 20/54 (37) | 23/44 (52) | 43/98 (44) |
Any child vitamin supplementation, n/N (%) | 30/48 (63) | 34/55 (62) | 30/46 (65) | 64/101 (63) |
Completed immunizations to date, n/N (%) | 48/49 (98) | 54/55 (98) | 43/47 (91) | 97/102 (95) |
Age at time of assessment (months), median (IQR) | 37.9 (36.9, 39.9) | 37.1 (36.5, 38.8) | 37.4 (36.5, 39.5) | 37.3 (36.5, 39.0) |
Child Fitzpatrick skin score grade 3–6, n (%) | 29/42 (69) | 34/48 (71) | 29/43 (67) | 63/91 (69) |
Child BMI Z score age 3, mean (SD) | 0.51 (1.48) | 0.35 (1.15) | 0.62 (1.15) | 0.47 (1.15) |
Child outdoors >1 hour/day, n/N (%) | 32/48 (67) | 34/53 (64) | 33/45 (73) | 67/98 (68) |
Child TV/computer >2 hours/day, n/N (%) | 24/48 (50) | 18/53 (34) | 17/45 (38) | 35/98 (36) |
Child 25(OH)D (nmol/L) age 3, median (IQR) | 42 (27, 68) | 35 (21, 66) | 42 (30, 93) | 41 (26, 72) |
Data shown are for all participants analysed.
IQR = interquartile range, SD = standard deviation, GA = gestational age, SCBU = Special Care Baby Unit, BMI = Body mass index.
We found no significant difference in the primary outcome of ‘wheeze ever’ between treatment groups (any vitamin D vs. control
Control | Combined vitamin D | RR | OR | aOR |
|||
(%) | (%) | (95% CI) | (95% CI) | (95% CI) | |||
Wheeze ever | 14/50 (28) | 26/108 (24) | 0.86 (0.49, 1.50) | 0.82 (0.38, 1.74) | 0.60 | 0.73 (0.33, 1.65) | 0.45 |
Recurrent wheezing | 7/50 (14) | 17/108 (16) | 1.12 (0.50, 2.54) | 1.15 (0.44, 2.97) | 0.77 | 1.14 (0.42, 3.13) | 0.80 |
Wheezing in the last year | 8/50 (16) | 17/108 (16) | 0.98 (0.46, 2.13) | 0.98 (0.39, 2.45) | 0.97 | 0.95 (0.36, 2.51) | 0.92 |
Wheeze with positive API | 7/50 (15) | 15/107 (14) | 1.00 (0.44, 2.30) | 1.00 (0.38, 2.64) | 1.00 | 1.06 (0.37, 3.02) | 0.91 |
Any bronchodilator use | 4/49 (8) | 24/104 (23) | 2.83 (1.04, 7.71) | 3.37 (1.10, 10.34) | 0.03 |
3.14 (0.96, 10.28) | 0.06 |
Eczema ever | 15/49 (31) | 30/102 (29) | 0.96 (0.57, 1.61) | 0.75 (0.35, 1.62) | 0.47 | 0.72 (0.32, 1.61) | 0.42 |
Eczema in the last year | 7/49 (14) | 20/103 (19) | 1.36 (0.62, 3.00) | 1.34 (0.52, 3.47) | 0.55 | 1.52 (0.55, 4.21) | 0.42 |
Atopy | 7/27(26) | 11/68 (16) | 0.62 (0.27, 1.44) | 0.56 (0.19, 1.66) | 0.30 | 0.29 (0.07, 1.16) | 0.08 |
Allergic rhinitis | 7/49 (14) | 11/101 (12) | 0.76 (0.31, 1.85) | 0.63 (0.22, 1.78) | 0.38 | 0.69 (0.22, 2.13) | 0.52 |
Food allergy diagnosis | 3/49 (6) | 12/102 (12) | 1.92 (0.57, 6.50) | 1.81 (0.48, 6.85) | 0.38 | 1.93 (0.45, 8.29) | 0.38 |
>4 URTI/year | 7/50 (14) | 20/103 (19) | 1.39 (0.63, 3.06) | 1.43 (0.55, 3.68) | 0.46 | 1.34 (0.49, 3.68) | 0.57 |
LRTI ever | 11/50 (22) | 31/101 (31) | 1.40 (0.77, 2.54) | 1.47 (0.64, 3.37) | 0.37 | 1.60 (0.67, 3.85) | 0.29 |
Primary health care records | |||||||
Recurrent wheeze | 3/31 (10) | 10/70 (14) | 1.48 (0.44, 5.00) | 1.56 (0.40, 6.10) | 0.52 | 1.47 (0.33, 6.55) | 0.61 |
Eczema | 6/31 (19) | 10/70 (14) | 0.74 (0.29, 1.85) | 0.46 (0.23, 2.12) | 0.52 | 0.63 (0.18, 2.16) | 0.46 |
Food allergy | 2/31 (6) | 2/70 (3) | 0.44 (0.07, 3.00) | 0.43 (0.06, 3.18) | 0.58 | 0.14 (0.00, 4.39) | 0.26 |
RR = risk ratio, OR = unadjusted odds ratio, aOR = adjusted odds ratio, API = Asthma predictive index, URTI = upper respiratory tract infection, LRTI = lower respiratory tract infection.
Model adjusted for mother’s ethnic group, presence of household smokers, maternal smoking in pregnancy, exclusive breast-feeding to four months, any parental allergic history, any child vitamin supplementation, number of children in the household, age mother left full-time education and baseline concentration of 25(OH)D in maternal blood. n = 139 for primary outcome measure.
Adjusted p-value for multiple testing non-significant at 20% level.
Control | Daily Vitamin D | RR | OR | aOR |
|||
(%) | (%) | (95% CI) | (95% CI) | (95% CI) | |||
Wheeze ever | 14/50 (28) | 11/56 (20) | 0.70 (0.35, 1.40) | 0.63 (0.26, 1.55) | 0.31 | 0.56 (0.20, 1.57) | 0.27 |
Recurrent wheezing | 7/50 (14) | 8/56 (14) | 1.02 (0.40, 2.61) | 1.02 (0.34, 3.06) | 0.97 | 1.11 (0.32, 3.92) | 0.87 |
Wheezing in the last year | 8/50 (16) | 8/56 (14) | 0.89 (0.36, 2.20) | 0.88 (0.30, 2.54) | 0.81 | 0.88 (0.27, 2.90) | 0.84 |
Wheeze with positive API | 7/50 (14) | 6/56 (11) | 0.77 (0.28, 2.13) | 0.74 (0.23, 2.36) | 0.61 | 0.65 (0.15, 2.82) | 0.57 |
Any bronchodilator use | 4/49 (8) | 10/56 (18) | 2.23 (0.75, 6.67) | 2.45 (0.72, 8.37) | 0.15 | 2.24 (0.54, 9.33) | 0.27 |
Eczema ever | 15/49 (31) | 15/54 (28) | 0.91 (0.50, 1.66) | 0.87 (0.37, 2.04) | 0.75 | 0.61 (0.23, 1.67) | 0.34 |
Eczema in the last year | 7/49 (14) | 11/55 (20) | 1.40 (0.59, 3.33) | 1.50 (0.53, 4.23) | 0.44 | 1.31 (0.38, 4.54) | 0.67 |
Atopy | 7/27 (26) | 4/36 (11) | 0.41 (0.13, 1.27) | 0.36 (0.09, 1.38) | 0.13 | 0.36 (0.05, 2.94) | 0.34 |
Allergic rhinitis | 7/49 (14) | 7/55 (13) | 0.89 (0.34, 2.36) | 0.88 (0.28, 2.70) | 0.82 | 0.63 (0.17, 2.36) | 0.49 |
Food allergy diagnosis | 3/49 (6) | 8/55 (15) | 2.38 (0.67, 8.46) | 2.61 (0.65, 10.45) | 0.16 | 4.53 (0.52, 39.33) | 0.17 |
>4 URTI/year | 7/50 (14) | 11/55 (20) | 1.43 (0.60, 3.40) | 1.54 (0.55, 4.33) | 0.42 | 1.39 (0.41, 4.68) | 0.60 |
LRTI ever | 11/50 (22) | 14/54 (26) | 1.18 (0.59, 2.35) | 1.24 (0.50, 3.07) | 0.64 | 1.00 (0.35, 2.91) | 1.00 |
Primary health care records | |||||||
Recurrent wheeze | 3/31 (10) | 4/36 (11) | 1.15 (0.28, 4.74) | 1.17 (0.24, 5.67) | 0.85 | 1.43 (0.21, 9.89) | 0.71 |
Eczema | 6/31 (19) | 5/36 (14) | 0.72 (0.24, 2.12) | 0.67 (0.18, 2.46) | 0.55 | 0.61 (0.13, 2.86) | 0.53 |
Food allergy | 2/31 (7) | 2/36 (6) | 0.86 (0.13, 5.76) | 0.85 (0.11, 6.44) | 0.88 |
RR = Risk ratio, OR = unadjusted odds ratio, aOR = adjusted odds ratio, API = Asthma predictive index, URTI = upper respiratory tract infection, LRTI = lower respiratory tract infection.
Model adjusted for mother’s ethnic group, presence of household smokers, maternal smoking in pregnancy, exclusive breast-feeding to four months, any parental allergic history, any child vitamin supplementation, number of children in the household, age mother left full-time education and baseline concentration of 25(OH)D in maternal blood.
Control | Bolus Vitamin D | RR | OR | aOR |
|||
(%) | (%) | (95% CI) | (95% CI) | (95% CI) | |||
Wheeze ever | 14/50 (28) | 15/52 (29) | 1.03 (0.56, 1.91) | 1.04 (0.44, 2.47) | 0.93 | 1.17 (0.44, 3.10) | 0.75 |
Recurrent wheezing | 7/50 (14) | 9/52 (17) | 1.24 (0.50 (3.07) | 1.29 (0.44, 3.77) | 0.65 | 1.91 (0.53, 6.75) | 0.31 |
Wheezing in the last year | 8/50 (16) | 9/52 (17) | 1.08 (0.45, 2.58) | 1.10 (0.39, 3.12) | 0.86 | 1.29 (0.40, 4.15) | 0.66 |
Wheeze with positive API | 7/50 (14) | 9/51 (18) | 1.26 (0.51, 3.12) | 1.32 (0.45, 3.86) | 0.62 | 2.01 (0.58, 6.99) | 0.27 |
Any bronchodilator use | 4/49 (8) | 14/48 (29) | 3.57 (1.27, 10.09) | 4.63 (1.40, 15.34) | 0.008 |
5.43 (1.39, 21.20) | 0.02 |
Eczema ever | 15/49 (31) | 15/48 (31) | 1.02 (0.56, 1.85) | 1.03 (0.44, 2.44) | 0.95 | 0.86 (0.32, 2.28) | 0.76 |
Eczema in the last year | 7/49 (14) | 9/48 (19) | 1.31 (0.53, 3.24) | 1.39 (0.47, 4.08) | 0.55 | 1.97 (0.47, 8.27) | 0.36 |
Atopy | 7/27 (26) | 7/32 (22) | 0.84 (0.34, 2.11) | 0.80 (0.24, 2.66) | 0.72 | 0.31 (0.05, 1.83) | 0.20 |
Allergic rhinitis | 7/49 (14) | 4/46 (9) | 0.61 (0.19, 1.94) | 0.57 (0.16, 2.10) | 0.40 | 0.91 (0.20, 4.11) | 0.90 |
Food allergy diagnosed | 3/49 (6) | 4/47 (9) | 1.36 (0.32, 5.78) | 1.43 (0.30, 6.75) | 0.65 | 1.31 (0.24, 7.18) | 0.76 |
>4 URTI/year | 7/50 (14) | 9/48 (19) | 1.34 (0.54, 3.31) | 1.42 (0.48, 4.17) | 0.53 | 1.72 (0.49, 6.04) | 0.39 |
LRTI ever | 11/50 (22) | 17/47 (36) | 1.64 (0.86, 3.14) | 2.01 (0.82, 4.92) | 0.12 | 2.87 (1.03, 8.03) | 0.05 |
Primary health care record | |||||||
Recurrent wheeze | 3/31 (10) | 6/34 (18) | 1.82 (0.50, 6.68) | 2.00 (0.46, 8.80) | 0.35 | 1.85 (0.36, 9.66) | 0.47 |
Eczema | 6/31 (19) | 5/34 (15) | 0.76 (0.26, 2.24) | 0.72 (0.20, 2.64) | 0.62 | 0.63 (0.11, 3.59) | 0.60 |
Food allergy | 2/31 (7) | 0/34 (0) | 0.0 (-, -) |
Bolus vitamin D versus control.
RR = Risk Ratio, OR = unadjusted odds ratio, aOR = adjusted odds ratio, API = Asthma predictive index, URTI = upper respiratory tract infection, LRTI = lower respiratory tract infection.
Model adjusted for mother’s ethnic group, presence of household smokers, maternal smoking in pregnancy, exclusive breast-feeding to four months, any parental allergic history, any child vitamin supplementation, number of children in the household, age mother left full-time education and baseline concentration of 25(OH)D in maternal blood.
Adjusted p-value for multiple testing non-significant at 20% level.
Since 22 offspring were not followed up, sensitivity analyses were performed to determine if this influenced the result for the primary outcome. Two scenarios were considered – the first where no drop-outs wheezed and the second where all drop-outs wheezed (Table S4 in
For 122 children assessed at 3 years, cord blood 25(OH)D levels were available. We found no difference between the natural logarithm (Ln) of cord blood 25(OH)D levels in children with and without a history of wheeze, atopy, eczema, any LRTI or >4 episodes of URTI per year (Table S5 in
Fifty-one of 180 (28%) children provided acceptable IOS data for analyses. We found no significant difference between groups in baseline respiratory resistance at 10 or 20 Hz, resonant frequency, area under the reactance curve or percentage response of these parameters to bronchodilator, when data were analysed for the two forms of prenatal vitamin D supplementation combined (Table S6 in
Horizontal bars represent means. No significant difference between groups.
Horizontal bars represent means. No significant difference between groups.
Total IgE levels, eNO and eosinophil counts were available for 106/180 (59%), 62/180 (34%) and 80/180 (44%) of offspring. We found no significant difference between groups in these outcomes assessed at age 3, when analysed for the two forms of prenatal vitamin D supplementation combined (Table S7 in
Ln IgE (A; n = 86), eNO (B; n = 62), and Ln eosinophil count (C; n = 90). Control versus daily and bolus vitamin D. Horizontal bars represent means. No significant difference between groups.
No adverse events related to treatment were reported in the offspring.
In this randomised controlled trial of vitamin D supplementation in late pregnancy in a relatively deficient mixed race population, daily supplementation with 800 IU ergocalciferol or a single bolus dose of 200,000 IU cholecalciferol from 27 weeks gestation did not prevent wheezing, allergic disease or influence measures of lung function or allergic inflammation in offspring in the first three years of life. We were unable to confidently exclude an effect on some secondary outcome measures such as atopy at 3 years, where statistical power was limited. Our results suggest that the most likely explanation for the finding of decreased wheezing risk in offspring of mothers with a higher vitamin D intake during pregnancy in observational studies
Our study has a number of limitations. First, we relied on a subjective primary outcome measure and participants were not blind to treatment allocation, which introduces a risk of reporter bias. Investigators were, however, kept blind to treatment allocation until database lock. Moreover the results of subjective primary outcome measures were supported by the results of both our secondary objective outcome assessments and a blinded assessment of prospectively recorded healthcare records. Second, this was a small study with limited statistical power, particularly for detecting differences in objective outcomes. Our power calculation was based on the study by Camargo et al
Finally, we are also unable to exclude the possibility that vitamin D supplementation at a higher dose, might protect against early childhood wheezing. Although the vitamin D doses used in this trial were greater than the current recommended intake for pregnant women of 400 IU/day during pregnancy in the United Kingdom
Two recent observational studies that documented prenatal vitamin D status by measuring cord blood 25(OH)D concentration, found relationships with allergic sensitisation and/or wheezing in early childhood
The findings of our study are specific to a population of vitamin D deficient women (half had baseline 25(OH)D levels below 25 nmol/L) and two specific forms of prenatal vitamin D supplementation. The doses of supplementation were chosen pragmatically, were not stratified based on individual vitamin D status or genotype, and response to treatment was not monitored before delivery. The study population was not selected for allergy or asthma risk and, as a mixed race urban population, is representative of many populations of pregnant women worldwide
In summary we found no evidence for a protective effect of prenatal vitamin D supplementation from 27 weeks gestation on childhood wheezing, allergic disease, lung function or markers of airway inflammation in the first 3 years of life. Given the modest effects on cord blood vitamin D achieved by these interventions, the safety and efficacy of higher dose prenatal vitamin D supplementation strategies need to be explored.
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We are grateful to our research nurses Heather Hanna, Katherine Phillips, Bridget Catterall, Louise Cross and Imperial College London undergraduates Megan Griffiths, Upama Bannerjee, Klara Vosicka, Anjali Thakari and Harsita Patel for their help with follow up assessments, to the late Michael Goldman for his advice on IOS quality control and to all the children and families for contributing their time to participate in this study.