Vitamin D status and supplementation in Antarctica: a systematic review and meta- analysis

Figures & data

Figure 1. Flow diagram of the study selection process

Figure 2. Antarctic bases of eligible studies. Referential map about locations of Antarctic bases and stations involved in studies included in the systematic review and meta-analysis

Table 1. Summary of findings. Characteristics of studies included in the systematic review and meta-analysis involved in 25(OH)D status

First author	Publication year	Antarctic base	Latitude (S)	Enrolment year	Country	Study type	Age (mean±SD or range) (years)	Follow-up length (estimated days)	25(OH)D measurement techniques	Number of study subjects	Sex (no. male/female)	BW or BMI (mean ± SD or/and range)	Main conclusions
Fairney, A.	1979	Halley Bay	75° 31’	Data not reported	UK	Prospective	21–39	Up to 456	Competitive binding protein assay	10	10/0	Data not reported	↓ 25(OH)D after an extended stay in Antarctica.
Lisbona, A.	1992	Juan Carlos I	62° 39ʹ	1988–1989	Spain	Controlled trial	28–45	22	Competitive protein binding assay	11	11/0	Data not reported	↓ 25(OH)D after a very short residence in Antarctica.
Wilske, J.	1993	Aurora expedition to Filchner Ice Shelf	75° 00ʹ	1991–1992	Uruguay	Prospective	Data not reported	90	Data not reported	4	Data not reported	Data not reported	↑ 25(OH)D after summer expedition.
Oliveri, MB.	1994	Belgrano II San Martin	77° 52ʹ 68° 07’	1990–1991	Argentina	Prospective	32 ± 4	365	Competitive protein binding assay	9	9/0	Data not reported	↓ 25(OH)D and did not increase even at the onset of summer.
Pitson, G.	1996	Davis	68° 34ʹ	1991	Australia	Prospective	33 ± 6	273	Competitive protein binding assay	19	19/0	81 (66–97) Kg	↓ 25(OH)D for each of the latter three sampling periods.
Yonei, T.	1999	Syowa	69° 00’	1995	Japan	Prospective	35 ± 7	365	Competitive protein binding assay	31	31/0	66.0 ± 6.3 (57–80) Kg	↓ 25(OH)D after an extended stay in Antarctica.
Oliveri, MB.	1999	Belgrano II	77° 52ʹ	1992	Argentina	Prospective	30 ± 5*	365–425	Competitive protein binding assay	10	10/0	24.6 ± 2.3 (kg/m^2)	↓ 25(OH)D in autumn and winter and recovered the initial level by the end of the campaign.
Iuliano-Burns, S.	2009	Casey Mawson Davis Macquarie Island (sub- antarctic station)	66° 16ʹ 67° 35ʹ 68° 57ʹ 54° 30’	2004–2006	Australia	Prospective	40 ± 11	365	Chemilum-nescent immunoassay	120	101/19	27 (kg/m^2)	Staying in the white continent produces vitamin D insufficiency for volunteers with vitamin D sufficiency at baseline (>50 nmol/L), unless baseline values were >100 nmol/L.
Premkumar, M.	2013	Maitri base	70º 45’	2010–2011	India	Prospective	39 ± 10	365	Radioimmunoassay	20	20/0	Data not reported	↓ 25(OH)D after an extended stay in Antarctica. Low dietary intake reduces serum 25(OH)D levels.
Steinach, M.	2015	Neumayer II and III	70° 65ʹ	2007–2012	Germany	Prospective	37 ± 91	395	ELISA	17	11/6	24.8 ± 3.3 (kg/m^2)	↓ 25(OH)D unaffected by age, gender, baseline fat mass, and station residence

*Mean of 17 volunteers, but 25(OH)D was assessed only in 10 volunteers. SD = standard deviation; BW = Body Weight; BMI = Body mass index.

Table 2. Summary of findings of studies evaluating the effect of VD supplementation on VD status

First author	Publicationyear	Antarctic base	Latitude (S)	Intervention dates	Age (mean±SD or range)	Country	Studytype	Intervention	Number of study subjects	Sex (no. male/female)	BW or BMI (mean ± SD or/and range)	Follow-up length (estimated days)	25(OH)D measurement assay	Main conclusions
Lisbona, A.	1992	Juan Carlos I	62° 39ʹ	1988–1989	28–49	Spain	Controlledoral VD3 supplementation	1,000 IU daily vs no intervention	7–11 per study arm	11/0	Data notreported	22	Competitive protein binding assay	VD3 oralsupplementation did not increase serum 25(OH)D level significantly.
Oliveri, MB.	1999	Belgrano II	77° 52ʹ	May 1992 to January 1993	30 ± 5*	Argentina	Open-labeloral VD supplementation	(1) average 100 IU daily during May andapproximately 125 IU daily from July to January	10	10/0	24.6 ± 2.3 (kg/m^2)	210	Competitive protein binding assay	After a decrease in 25(OH)D serum level during a 5-month residency in Antarctica, oral supplementation with VD during at least six months allows a recovery to the baseline level of 25(OH)D
Smith, S.	2009	McMurdo	77° 51ʹ	March to August 2007	(1) 42 ± 12 (2) 44 ± 12 (3) 43 ± 12	USA	Randomised double-blind oral VD3 supplementation	(1) 2,000 IU daily (2) 1,000 IU daily (3) 400 IU daily	(1) 18 (2) 19 (3) 18	41/14	(1) 28 ± 6 (2) 31 ± 7 (3) 29 ± 6 (kg/m^2)	150	Radioimmuno-assay	Five months after supplementation started, 25(OH)D increased in all supplemented groups
Zwart, S.	2011	McMurdo	77° 51’	February toSeptember 2009	(1) 37 ± 10 (2) 45 ± 10	USA	Controlled oral VD3 supplementation	2,000 IU daily or 10,000 IU weekly	(1) 15 (2) 14	(1) 9/6 (2) 12/2	(1) 28 ± 4 (2) 29 ± 4 (kg/m^2)	180	Radioimmuno-assay	Doses administered increased vitamin D level, and efficacy was influenced by baseline vitamin D status and BMI.
Iuliano-Burns, S.	2012	Casey, Mawson, Davis, Macquarie Island	66° 16ʹ 67° 35ʹ 68° 57ʹ 54° 30’	Summer 2007 to 2008 or Summer 2008 to 2009	(1) 42 ± 11 (2) 40 ± 11 (3) 43 ± 12		Randomised double-blind oral VD3 supplementation	(1) 50,000 IU monthly, (2) 50,000 IU every two months and placebo on alternate months, (3) 50,000 IU single dose pre-departure and monthly placebo thereafter	(1) 37 (2) 38 (3) 35	(1) 31/6 (2) 31/7 (3) 32/3	(1) 23.7 (2) 27.2 (3) 27.9 (kg/m^2)	Up to 365	Electrochemi-luminesceimmunoassay	25(OH)D level can be maintained at sufficiency status with an oral dose of 50,000 IU at least every alternate month during residence in Antarctica.

*Mean of 17 volunteers, but 25(OH)D was assessed only in 10 volunteers; IU = international units; SD = standard deviation; VD3 = vitamin D3; BMI = Body mass index; BW = Body Weight

Figure 3. Assessment of risk of bias in included studies

Figure 4. Meta-analysis of 25(OH)D serum change pre- and post- Antarctic residence in non-supplemented subjects. A) Mean difference forest plot of 25(OH)D. The mean differences were calculated based on 25(OH)D serum level at baseline and after a completed stay on the Antarctic or sub-Antarctic bases. The studies of Lisbona, A. 1992 and Iuliano-Burns, S. 2012 are included only with the non-interventional group. Values represent the mean effect sizes within a study. B) Funnel plot for publication bias. SE: Standard error of the mean difference

Figure 5. Comparison of 25(OH)D before and after a summer stay in Antarctica in subjects not receiving vitamin D supplementation. A) Mean difference forest plot of 25(OH)D. The mean differences were calculated based on 25(OH)D serum level at baseline and after at least 22 days of stay among December and February. Values represent the mean effect sizes within a study. B) Funnel plot for publication bias. SE: Standard error of the mean difference

Figure 6. Comparison of 25(OH)D before and after overwintering in Antarctica in subjects not receiving vitamin D supplementation. A) Mean difference forest plot of 25(OH)D. The mean differences were calculated based on 25(OH)D serum level at baseline and after a residence between March and September. Values represent the mean effect sizes within a study. B) Funnel plot for publication bias. SE: Standard error of the mean difference

Figure 7. Meta-analysis of the effect of VD supplementation on serum 25(OH)D concentrations during Antarctic residence. A) Mean difference forest plot of the effect of VD supplementation. The mean differences were calculated based on 25(OH)D serum level at baseline and after Antarctic residence in the supplemented groups. Values represent the mean effect sizes within a study. B) Funnel plot for publication bias. SE: Standard error of the mean difference