Global Perspective of the Vitamin D Status of African-Caribbean Populations: A Systematic Review and Meta-analysis

Systematic review

The initial search resulted in 2204 papers. After duplicates were removed, 1507 papers were screened by title and abstract. Finally, the full text of 247 papers were screened [23] (See Fig. 1 for PRISMA flow diagram). For reasons for exclusion, see the Supplementary File and Table 4.

**Fig. 1: PRISMA flow diagram showing study selectionAQ5 process [23].**

Nineteen observational studies, exploring the vitamin D status or dietary intake of the AfC population across six countries with different latitudes were included (n = 5670 participants) (see Tables 1 and 2). Jackson et al. [33] reported on both 25(OH)D concentration and dietary intake, so is included in both the 25(OH)D and dietary intake qualitative analyses (see Supplementary File and Table 5). The studies varied in terms of quality, with most studies being considered fair to good quality (Supplementary File and Tables 6 and 7). The included papers were all published in the previous 15 years, from 2005 to 2019.

Table 1 Summary table for 25(OH)D concentrations of African-Caribbean populations.

Table 2 Summary table for vitamin D dietary intake of African-Caribbean populations.

25(OH)D concentration of African-Caribbeans living in low latitudes (0–37° North and South)

Ten of the included papers explored the 25(OH)D of an AfC population living at low latitudes (Caribbean islands), with high year-round sun exposure (n = 3209 participants) [9, 17, 21, 33,34,35,36,37,38,39]. All of these studies reported AfC participants to have ‘sufficient’ vitamin D levels according to assigned cut-offs, as stated by the study authors. As an exception, Velayoudom-Cephise et al. [39] described their AfC participants with T2DM as having ‘insufficient’ vitamin D levels, with a mean 25(OH)D concentration of 54.16 ± 17.22 nmol/L. The study found ‘deficiency’ (<50 nmol/L) in 42.6% of the population, despite sunny climates [39]. Similarly, Foucan et al. [36] found ‘insufficient’ (<75 nmol/L) 25(OH)D concentration (mean 70.29 ± 26.51 nmol/L) in their population of haemodialysis patients.

AfC populations living close to the equator had higher 25(OH)D concentrations when compared to their non AfC counterparts [34, 38, 39]. For example, Barbour et al. [34] found AfCs living in the Caribbean had significantly higher 25(OH)D concentrations compared to those with White European ancestry living in the US (86.61 ± 24.21 vs. 68.89 ± 20.72 nmol/L, p < 0.001). Similarly, Foucan et al. [36] found that AfC dwelling close to the equator had lower rates of vitamin D ‘insufficiency’ when compared to a previous study with African Americans (AA) living in United States of America (US) (60% vs 80% respectively, p < 0.001) [40]. Likewise, a study by Naqvi et al. [38] found a higher concentration of 25(OH)D in AfC compared to the Indigenous Mayan population, living in the Caribbean islands (74.38 ± 19.82 nmol/L vs. 64.47 ± 14.55 nmol/L).

Three of these studies reported on the results of the Vitamin D Ancillary Study (VIDA) [9, 35, 41]. This study compared participants of African ancestry living at different latitudes and found, according to author defined cut-offs, 90% of AfC participants living in Jamaica (17°N) to have ‘sufficient’ vitamin D levels, and none to be deficient [9, 35, 41]. Interestingly, they also found, a negative correlation between latitudinal distance from the equator and 25(OH)D concentrations, with those of African ancestry living in Jamaica (17°N) having a higher vitamin D concentration when compared to those with African ancestry living in the US (41°N) (72.13 ± 17.72 nmol/L vs 42.93 ± 19.96 nmol/L) [9, 35, 41].

25(OH)D concentration of African-Caribbeans living in mid to high latitudes (37–90° North and South)

Four studies explored the vitamin D status of AfC populations living at higher latitudes (UK and US) (n = 995 participants) [27, 42,43,44]. One study was carried out in the US (41°N) [42], whilst the other three were in the UK (52–53°N) [27, 43, 44]. In contrast to AfC populations living at low latitudes, these studies found the mean 25(OH)D concentration of their participants to be ‘insufficient’ to ‘deficient’ according to differing author assigned cut-offs, ranging from 28.0 ± 2.0 to 56.66 ± 20.97 nmol/L [27, 42,43,44], whilst according to our pre-determined cut-offs, the participants were vitamin D insufficient [27, 43, 44] or sufficient [42].

Of the three studies that compared an AfC population to a White Europeans (WE) population, living in the same location, found higher concentrations of 25(OH)D in the WE population [42,43,44]. Crew et al. [42] found that higher levels of 25(OH)D were associated with WE ethnicity. Ford et al. [43] reported that WE had the highest mean levels of 25(OH)D, followed by AfCs and then South Asians. Of note, this study also showed that one in every four AfCs living in the UK (52° N) were vitamin D ‘deficient’, according to the author’s definition (<25 nmol/L) after summer [43]. Likewise, Rezai et al. [44] reported a deficient (<50 nmol/L) mean 25(OH)D of 28 ± 2 nmol/ in their AfC sample, which was a 14 nmol/L lower than the mean concentration of their WE counterparts (p < 0.001). Patel et al. [27] found that only 15.4% of AfC participants living in the UK had adequate vitamin D levels (defined as >50 nmol/L).

We found a strong inverse association (Pearson’s correlation) between 25(OH)D status and distance from the equator (r = −0.894, p < 0.0001) across the 12 papers [17, 21, 33,34,35,36,37,38,39, 42,43,44] included in the sub sample that measured 25(OH)D at different latitudes (Fig. 2).

**Fig. 2: Relationship between vitamin concentration [25(OH)D] and latitude in the African-Caribbean population.**

Vitamin D dietary intake at low latitudes 0–37° North and South

Three studies measured vitamin D dietary intake in AfC populations living close to the equator (Caribbean islands) (n = 782 participants) [33, 41, 45]. The studies varied in terms of the tools used to measure intake, including food frequency questionnaire [33, 45], a 24 h food recall [41] and a 4-day food diary [45]. The Caribbean islands have a low recommended dietary allowance (RDA) for vitamin D of 2.5 µg/day [29]. Although intakes were low, ranging from 1.0 to 3.7 µg/day of vitamin D, two studies had ‘sufficient’ mean intakes when compared to the local RDA for this population [33, 41]. However, in another study, the mean intake of vitamin D for Caribbean island participants with breast or prostate cancer did not meet recommendations [45]. This may be partly explained by the fact that these research participants had cancer, so may not have had normal food intake.

Vitamin D dietary intake at high latitudes 37–90° North and South

Three studies measured dietary intake of vitamin D at high latitudes (all in the UK) (n = 621 participants) [26, 46, 47]. All studies included used a 24-h recall to assess dietary intake [26, 47], whilst in addition, Castaneda-Gameros et al.[46] also used a dietary review. The UK recommended nutrient intake (RNI) for vitamin D is 10 µg/day [22]. Low vitamin D dietary intake was seen in all the studies, ranging from 1.7 to 9.6 µg/day. A study of n = 40 post-partum mothers by Rees et al. [26], found that AfC women living in the UK, although having low intakes of vitamin D, still reported slightly higher mean intakes than those of WE or Asian ancestry. Conversely, in another study, inadequate dietary vitamin D was seen in AfC children (1.71 µg/day), with intakes lower than that of their WE counterparts (1.9 µg/day), but higher than those of South Asian children (1.4 µg/day) [47]. A small study by Castaneda-Gameros et al. in older migrant women of mixed ethnicity found vitamin D to be a nutrient of concern, with a median intake of 2.6 µg/day (IQR 0.7–11.4), significantly lower than the UK RNI (p = 0.02). However, in a sub sample (n = 21) of AfC women, in the same study, unpublished data provided by the authors showed a mean intake of 9.6 µg/day vitamin D, which, included participants who used vitamin D containing supplements [46].

Meta-analysis

Sixteen studies were included in the meta-analysis, which involved analysis of 25(OH)D concentration [17, 21, 33,34,35,36,37,38,39, 42,43,44] and vitamin D dietary intake [33, 41, 45,46,47] of AfC populations living at different latitudes. Jackson et al. [33] reported on both 25(OH)D and dietary intake. The remaining three studies were excluded due to insufficient data [26, 27] or reporting on the same data as another author, in which case the study published first was used [9].

25(OH)D concentration

Twelve studies reported 25(OH)D concentration (n = 2974 participants) [17, 21, 33,34,35,36,37,38,39, 42,43,44]. The pooled effect size for 25(OH)D concentration in AfC populations was a mean_(random) of 67.8 nmol/L, 95% CI (57.9, 77.6), with statistically significant heterogeneity (P_{(heterogeneity)} < 0.001). A pooled mean_(fixed) of 73.5 nmol/L, 95% CI (72.7, 74.3) with statistically significant heterogeneity (P_{(heterogeneity)} < 0.001) was found in a fixed effects model.

A meta-analysis of 25(OH)D concentration in AfC populations living at high latitudes [27, 42,43,44] resulted in a pooled mean_(random) of 40.9 nmol/L, 95% CI (28.1, 53.7) and a pooled mean_(fixed) of 36.0 nmol/L, 95% CI (33.4, 38.7). At low latitudes [9, 17, 21, 33,34,35,36,37,38,39], a pooled mean_(random) of 76.4 nmol/L, 95% CI (68.6, 84.3) and a pooled mean_(fixed) of 77.3 nmol/L, 95% CI (76.5, 78.1) was found. Statistically significant heterogeneity was present in all models (p < 0.001) (see Fig. 3 for random effects models, and Supplementary File and Fig. 1 for fixed effects models).

**Fig. 3: Random effects meta-analyses of 25(OH)D concentration of the African-Caribbean population.**

Vitamin D dietary intake

Five studies reported on vitamin D dietary intake (n = 1363 participants) [33, 41, 45,46,47]. The pooled mean_(random) effect size for vitamin D dietary intake was 3.0 µg/day, 95% CI (1.67,4.31) with statistically significant heterogeneity (P_{(heterogeneity)}<0.001). In a fixed effect model, a pooled mean_(fixed) of 1.84 µg/day, 95% CI (1.75, 1.93) with statistically significant heterogeneity (P_{(heterogeneity)} < 0.001) was found.

For vitamin D intakes in populations living at high latitudes [46, 47], there was a pooled mean_(random) of 5.51 µg/day, 95% CI (−2.26, 13.3) and a pooled mean_(fixed) of 1.71 µg/day, 95% CI (1.61, 1.81). At low latitudes [33, 41, 45] a pooled mean_(random) of 2.38 µg/day, 95% CI (−0.112, 4.87) and a pooled mean_(fixed) of 2.68 µg/day, 95% CI (2.43, 2.93) was found. Statistically significant heterogeneity was present in all sub-group models (p < 0.001). A sensitivity analysis showed consistent results across all analyses (see Fig. 4 for random effects models, and Supplementary File and Fig. 2 for fixed effects models and Table 8 for the sensitivity analysis).