Bone mineral content among Inuit – a systematic review of data

ABSTRACT

Inuit are a distinct ethnic group living in an environment likely to influence calcium metabolism and skeletal health. Bone mineral content (BMC) is a marker of skeletal health and fracture risk. Age is a dominant risk factor for osteoporosis, emphasising the importance of skeletal health in the ageing Inuit populations. This systematic review aims to provide an overview of data on BMC among Inuit. We performed a systematic search for data on BMC among Inuit guided by an experienced librarian. The search identified 211 studies, of which six provided data on BMC among Inuit living in Alaska or Canada. In men/women, BMC peaked around the age of 25 years in distal radius at 1.55/1.07 g/cm2 and in distal ulna at 0.81/0.54 g/cm2. Diaphysis of ulna, humerus, and tibia peaked around 10 years later. The 23% to 30% sex differences in BMC were similar across studies. Age related changes were parallel to other populations. In conclusion, BMC in Inuit is presented for easy viewing and comparison. BMC was similar between Inuit populations, and sex and age-related differences were comparable to other populations. New scientific studies should update data, include spine and hip, describe bone structure, and consider fracture risk beyond BMC.

Introduction

Osteoporosis is a skeletal disorder characterised by low bone mass and microarchitectural deterioration leading to low bone strength, which may lead to fragility fractures causing pain, loss of mobility, nursing home admission, reduced quality of life, and premature death [1]. Osteoporosis is a severe chronic disease that becomes increasingly frequent as bone strength decreases [2]. Age is a dominant risk factor for osteoporotic fractures [3] as bone strength decreases with advancing age [4], adding to other risk factors such as diabetes and low calcium intake, and osteoporotic fractures are seen among one in three Caucasian women and one in six Caucasian men aged 65+ years [5]. Inuit populations are ageing with a steep rise in life expectancy and a focus on life for older people [6,7], causing an interest in osteoporosis risk among Arctic people.

A higher occurrence of hip fractures among Caucasian Americans than African Americans [8] inspired an analysis showing differences between Inuit and Caucasian populations in hip geometry [9] albeit differences in bone mineral density (BMD) were related to body size rather than ethnicity [10]. Still, Inuit and Caucasians also show marked differences in metabolism and type-2 diabetes [11], body build [12], autoimmunity [13], diet [14], and calcium metabolism [15]. In addition, Inuit have not adapted to dairy products as a source of calcium as illustrated by the lack of lactase persistence [16]. Hence, it may be hypothesised that calcium content of bones (bone mineral content; BMC) is low among Inuit.

Calcium metabolism among Inuit may have adapted to both the intake of local foods with a low calcium content, and to the vitamin D levels influenced by the traditional diet and the extremes of sun exposure that comes with Arctic residence. Both are of major importance for bone health, and hence, BMC in Inuit is a concern. Thus, this systematic review aims to provide an overview of data on BMC among Inuit.

Methods

The review complies with the Preferred Reporting of Items for Systematic Review and Meta-analysis (PRISMA) guidelines and we used Covidence for handling references. Systematic searches were performed in the main medical databases, Medline and Embase. The search string was constructed in collaboration with a research librarian with expertise in systematic reviews. The terms and keywords used were, Medline: (“Inuit”[MeSH Terms] OR “Greenland”[MeSH Terms] OR (“inuit*”[Title/Abstract] OR “eskimo*”[Title/Abstract] OR “inuk*”[Title/Abstract] OR “aleut*”[Title/Abstract] OR “inupiat*”[Title/Abstract] OR “kalaallit*”[Title/Abstract] OR “greenland*”[Title/Abstract])) AND (“Bone Density”[MeSH Terms] OR (“Osteoporosis”[MeSH Terms] OR “osteoporos*”[Title/Abstract]) OR ((“Bone and Bones”[MeSH Terms] OR “bone*”[Title/Abstract]) AND (“Minerals”[MeSH Terms] OR (“mineral*”[Title/Abstract] OR “densit*”[Title/Abstract] OR “loss”[Title/Abstract] OR “weight”[Title/Abstract] OR “content*”[Title/Abstract] OR “mass”[Title/Abstract])))); Embase: ((“eskimo-aleut people”/exp OR “greenland”/exp) OR (inuit*:ti,ab,kw OR eskimo*:ti,ab,kw OR inuk*:ti,ab,kw OR aleut*:ti,ab,kw OR inupiat*:ti,ab,kw OR kalaallit*:ti,ab,kw OR greenland*:ti,ab,kw)) AND (((“bone”/exp OR bone*:ti,ab,kw) AND (“mineral”/exp OR (mineral*:ti,ab,kw OR densit*:ti,ab,kw OR loss:ti,ab,kw OR weight:ti,ab,kw OR content*:ti,ab,kw OR mass:ti,ab,kw OR demineral*:ti,ab,kw))) OR osteoporos*:ti,ab,kw OR (“bone density”/exp OR “bone demineralization”/exp)).

All databases were searched from inception to 24 September 2024. Reference lists of included studies and relevant systematic reviews were manually searched and if needed, experts in the field were contacted to identify missing studies. We included relevant studies that used any design. No restriction on language, or publication date was imposed, but inclusion was restricted to studies on Inuit or Eskimo and techniques estimating BMC. We included both studies of living Inuit, cadavers, and those conducting analysis of skeletons. Studies onBMD were selected for full text reading to ensure the inclusion of all data on BMC, and to add depth to the discussion.

Study selection

Figure 1 is the PRISMA diagram illustrating the study selection process. Two reviewers (J.B.S.) and (T.M.H.) independently assessed the eligibility of articles by screening the titles and abstracts and then by reviewing the full texts of relevant articles. Disagreements were settled by consensus between reviewers or, if necessary, by consulting a third reviewer (S.A.).

Figure 1.

PRISMA diagram.

Results

Six papers were identified through the searching process. Mazess, 1974 and Mazess, 1975 with data from Alaska and Canada using direct photon absorptiometry on living subjects [17,18]. Harper, 1984, included data from Alaska using direct photon absorptiometry on living subjects [19]. Mazess, 1972, included data from Canada based on skeletons [20]. Thompson, 1981, included data from Greenland and Alaska using direct photon absorptiometry on cadavers [21]. Martin, 1985, included data from Alaska using direct photon absorptiometry on skeletons [22]. None of the studies performed on cadavers or skeletons provided an estimate of when they entered the ground.

The single-photon absorptiometry method applied in the studies by Harper et al. and Martin et al. used radioactive iodine-125 as a low-energy photon source [19,22]. This method had lower precision than today’s standard of dual-energy x-ray source (DEXA). Also, data on height or weight were not available in these studies and the relevant adjustment of BMC for body size could not be performed.

The data on BMC in Inuit is presented in Tables 1–3. Each table matches the anatomical location, and data is arranged as parallel lists of BMCs for the different studies, ordered by sex and age groups. Two papers by Mazess report data as g/cm in the original article, though the method described would produce results as g/cm² [17,18]. Radius-BMC is listed in Table 1, Ulna-BMC in Table 2, and Humerus-BMC in Table 3. The sex related difference ranged from 23% in Ulna diaphysis to around 30% in the distal part of Ulna, with similar data among Canadian and Alaskan Inuit.

Table 1.

Bone mineral content (mean BMC, g/cm2) in radius among Inuit men and women, with references in brackets.

		Radius
		Diaphysis										Distal epiphysis
	Age	Canada (18)		Alaska (17)		Alaska (19)			Canada (20)			Canada (18)		Alaska (17)
Males		n	BMC***	n	BMC***	n	BMC		n	BMC		n	BMC***	n	BMC***
	5–7	12	0.438	23	0.462	5	0.471					12	0.48	14	0.478
	8–9	24	0.477	19	0.536							24	0.472	9	0.554
	10–11	20	0.574	22	0.626	19	0.762					20	0.589	14	0.608
	12–14	20	0.710	20	0.76							20	0.749	13	0.769
	15–16	8	0.881	9	0.926	25	1.062					8	0.988	6	1.007
	17–19	10	1.055	15	1.163				15*	0,81**		10	1.234	7	1.397
	20–29	26	1.239	16	1.273	30	1.17					26	1.527	4	1.568
	30–39	19	1.169	17	1.2	11	1.193					19	1.419	7	1.433
	40–49	16	1.211	7	1.171	15	1.157		7*	0,726**		16	1.429	3	1.308
	50–59	12	1.063	13	1.125	8	1.097					12	1.221	19	1.213
	60–69	8	0.990	27	1.017	4	1.084					8	1.033	18	1.052
	70+			13	1.058	4	0.963							10	1.029
Females
	5–7	12	0.382	26	0.437	8	0.381					12	0.407	14	0.423
	8–9	12	0.432	22	0.483							12	0.466	13	0.438
	10–11	17	0.493	17	0.558	17	0.738					17	0.523	8	0.539
	12–14	20	0.673	22	0.762							20	0.702	8	0.712
	15–16	9	0.814	10	0.848	17	0.826					9	0.912	5	0.881
	17–19	13	0.823	12	0.878				19*	0,783**		13	0.973	8	0.969
	20–29	23	0.869	14	0.889	23	0.928					23	1.05	8	1.08
	30–39	24	0.873	19	0.928	17	0.823					24	1.009	10	0.964
	40–49	15	0.899	16	0.883	19	0.876		20*	0,667**		15	1.002	12	1.042
	50–59	11	0.775	23	0.782	12	0.814					11	0.912	10	0.935
	60–69	4	0.653	20	0.685	7	0.724					4	0.774	18	0.696
	70+			11	0.507	7	0.56							11	0.472

*Age group uncertain.

**No description of part of radius measured.

***Given as g/cm in the original article, though the method described would produce results as g/cm2. These results are in cursive.

Table 3.

Bone mineral content (mean BMC, g/cm2) in humerus among Inuit men and women, with references in brackets.

		Humerus – Diaphysis
	Age	Canada (18)
Males		n	BMC*
	5–7	9	0.974
	8–9	10	1.138
	10–11	8	1.432
	12–14	7	1.773
	15–16	3	1.982
	17–19	8	2.518
	20–29	12	2.76
	30–39	10	2.84
	40–49	4	2.748
	50–59	3	2.763
	60–69	9	2.336
Females
	5–7	12	0.917
	8–9	9	1.015
	10–11	9	1.106
	12–14	14	1.635
	15–16	5	1.898
	17–19	4	1.724
	20–29	6	1.82
	30–39	9	2.001
	40–49	4	1.911
	50–59	4	1.57
	60–69	0

*Given as g/cm in the original article, though the method described would produce results as g/cm2. These results are in cursive.

Table 2.

Bone mineral content (mean BMC, g/cm2) in ulna among Inuit men and women, with references in brackets.

		Ulna
		Diaphysis								Distal epiphysis
	Age	Canada (18)		Alaska (17)			Canada (20)			Canada (18)		Alaska (17)
Males		n	BMC**	n	BMC**		n	BMC		n	BMC**	n	BMC**
	5–7	12	0.372	23	0.402					12	0.266	14	0.271
	8–9	24	0.427	19	0.456					24	0.293	9	0.305
	10–11	20	0.493	22	0.543					20	0.321	14	0.33
	12–14	20	0.612	20	0.661					20	0.414	13	0.415
	15–16	8	0.743	9	0.817					8	0.518	6	0.52
	17–19	10	0.92	15	1.005		16*	0.893		10	0.633	7	0.712
	20–29	26	1.077	16	1.06					26	0.772	4	0.847
	30–39	19	1.034	17	1.067					19	0.743	7	0.721
	40–49	16	1.117	7	1.032		8*	0.860§		16	0.748	3	0.699
	50–59	12	0.96	13	1.066					12	0.676	19	0.656
	60–69	8	0.903	27	0.93					8	0.542	18	0.563
	70+			13	0.946							10	0.514
Females
	5–7	12	0.333	26	0.371					12	0.228	14	0.234
	8–9	12	0.385	22	0.412					12	0.254	13	0.236
	10–11	17	0.431	17	0.48					17	0.284	8	0.307
	12–14	20	0.597	22	0.642					20	0.37	8	0.368
	15–16	9	0.696	10	0.752					9	0.47	5	0.465
	17–19	13	0.737	12	0.767		19*	0.817		13	0.515	8	0.503
	20–29	23	0.776	14	0.793					23	0.543	8	0.528
	30–39	24	0.772	19	0.815					24	0.532	10	0.483
	40–49	15	0.804	16	0.811		20*	0.741		15	0.488	12	0.503
	50–59	11	0.728	23	0.712					11	0.469	10	0.47
	60–69	4	0.6	20	0.647					4	0.376	18	0.333
	70+			11	0.462							11	0.22

^§Likely typing error in the original table of 0.086.

*Age group uncertain.

**Given as g/cm in the original article, though the method described would produce results as g/cm2. These results are in cursive.

Data were extracted from studies in different geographical areas .Figure 2 is a map providing an overview of the Circumpolar area with the geographical location of each study providing BMC data on Inuit [17–20].

Figure 2.

Map of the Northern Hemisphere, showing Alaska (US), Canada and Greenland, marked with geographical locations of cited sources. This figure is based on ‘https://commons.wikimedia.org/wiki/File:Northern_Hemisphere_LamAz.png’. Use is permitted with attribution under the Creative Commons Attribution 2.0 generic license.

Data on femoral BMC in Greenland Inuit male/female skeletons (n = 31/32) was available in one study [21]. The average BMC was 3.470/2.799 gm/cm, while age was not determined in these skeletons. BMC of Tibia was measured in Alaskan Inuit (n = 141) and showed that the mean age of peak in BMC was 37 years for men and 36 years among women, and women’s BMC decreased by 50% between the third and sixth decade [22].

Figure 3 shows the age-related changes in BMC in Radius for each sex calculated from the studies among Canadian and Alaskan Inuit, with location noted on the map (Figure 2) [17,18]. Figure 3 illustrates that peak bone mass was reached around the age of 30 years followed by an accelerating age-related decline in BMC.

Figure 3.

Line graph of age-related changes in BMC meassured in Radius for men and women, based on data derived from studies of Inuit populations in Canada and Alaska.

Discussion

We identified six reports regarding BMC in Inuit, all from Alaska and Canada. Most data were published around half a century ago and data are now summarised and presented coherently. The data showed that peak bone mass occurred around the age of 30 years as illustrated for Radius, and the subsequent decrease was substantial.

The Inuit populations in Greenland are ageing with a rise in life expectancy of around 10 years for men and 6 years for women over the past 40 years [23]. This rise emphasises the importance of a focus on skeletal health as osteoporotic fractures are frequent among older people [3,24] and bone strength decreases with age [4]. Data identified and presented here for Inuit imply a substantial age-related decrease in BMC making osteoporosis an important topic for the ageing Inuit populations.

Bone mineral content of Inuit women was around 25% lower compared to Inuit men. This finding is in keeping with finding in other populations [4], and the similar sex-related differences among Inuit between geographical areas supports the validity of the finding. This finding is further supported by the higher frequency of osteoporotic fracture among women compared to men living in Greenland [25].

Ethnic groups may vary from each other on several physiological parameters. When comparing Caucasian Danes to Greenlandic Inuit differences have been described for metabolism [11], body build [12], and autoimmunity [13], in addition to the lack of lactase persistence [16] and a difference in calcium metabolism [15]. Hip geometry influences the risk of fracture as emphasised by findings in other ethnic groups. Nelson and colleagues found that the lower occurrence of hip fractures among African-Americans compared to Caucasians may be related to differences in hip geometry [26]. Hip geometry in Inuit and Scandinavians differed [9] and the risk of hip fractures may be influenced by Inuit ethnicity, even though differences in BMD between Inuit and Caucasians were related to body size rather than ethnicity [10]. Overall, very little data exists on fracture rate in indigenous peoples, including Inuit [27]. Hence, the influence of Inuit ethnicity for fracture risk remains to be settled.

The most recent study of BMC among Inuit living in North America was from 1984 [19], while updated studies measuring peripheral BMD using DEXA include a study published in 2005 among 80 Greenland Inuit men and women aged 30 through 49 years [28] and 568 postmenopausal women in Canada aged 40 through 90 years during 2007–2008 [29,30]. The findings from these recent studies using DEXA are in keeping with the studies on BMC reported in this review. Thus, the parallel findings among groups of Inuit support the validity of the findings despite most of the BMC studies were done on cadavers and skeletons, in which their time in the ground, exact age at death, and living conditions were uncertain.

Present-day Inuit are likely to differ in lifestyle, physical activity, and diet. Thus, comparison with present-day Inuit should be performed with caution. Indeed, dietary changes could have a major influence on calcium and vitamin D intake with adverse consequences for skeletal health. Hence, new data on BMC or BMD in Inuit are warranted extending the two studies of BMD among Inuit from North Greenland [28] and Canada [29]. The need for this data is further emphasised by the ageing Inuit populations with well-known ethnic differences in hip geometry [9] and calcium metabolism [15]. Still, the sparse populations scattered across the vast geography of the Arctic support the use of alternatives. These could be qualitative ultrasound measuring connectivity of trabecula in bone microarchitecture [31] or clinical risk factors for prediction of future fragility fracture [24] as the added value of measures of BMC may be limited [32].

The clinical aspect of skeletal health focuses on osteoporotic fractures with pain, immobilisation, and premature death, which is a point of notice by Inuit in Greenland [24]. The scattered geography of Arctic people suggests using other risk factors than BMC for evaluation of osteoporosis in everyday clinical practice. These risk factors include other diseases, such as hyperthyroidism, hyperparathyroidism, inflammatory bowel disease, rheumatoid arthritis, and heart failure as seen among people in Greenland [33]. In addition, diabetes raises the risk of fractures in European populations and the diabetic predisposition [34] with increasing prevalence of diabetes among Inuit [29,35,36] encourages evaluation of fracture risk among Inuit with diabetes.

Tools like QFracture and FRAX use clinical risk factors for assessment of the 10-year risk of fragility fracture [37]. While these tools are readily available to support clinicians on treatment decisions, studies to validate i.e. FRAX for use in Inuit populations are lacking, and this is a path for future research. Such studies should consider ethnic differences in both fragility fracture frequency, BMC and calcium metabolism.

Calcium homoeostasis is tightly controlled by powerful hormonal mechanisms. Interestingly, populations in Greenland may have low vitamin D but lack the parallel rise in parathyroid hormone seen in European populations [15]. This ethnic difference implies altered mechanisms in calcium homoeostasis that could be speculated to influence skeletal health [15,38,39]. These disparities inspire further evaluation of bone health including hormonal and metabolic parameters, and BMC.

Our review was strengthened by the systematic search for data on BMC guided by an experienced librarian and performed with no time or language restrictions. Thus, older studies were included, which introduced uncertainty of subjects’ comparability to current living Inuit. The inclusion of studies on cadavers and skeletons introduced further uncertainty of the Inuit under study in regards to how long they may have been buried before study. Another limitation is that data were mainly on peripheral bones. Thus, we found no data on BMC or BMD of the spine and limited data on femoral bone. This is relevant as the prediction of fracture risk at an anatomical site relates to BMC of that area. Hence, axial and femoral neck BMCs would be of interest in relation to osteoporotic fractures. Still, peripheral BMC is descriptive of bone health to be used in studies of bone metabolism. The studies included measured BMC using single photon absorptiometry, and the methods sections do not include data on accuracy or calibration in the field. The techniques for measuring BMC have improved since these studies were performed, and single photon absorptiometry has been replaced by DEXA for better precision. While this is important for measurements in individuals, the single photon measurements remain valid for assessing BMC in groups as presented in the present review. Accordingly, the data illustrate trends in BMC among groups, which conform to findings using present day gold standard of DEXA. As for measurement errors, present recommendation is a coefficient of variation of no more than 2% which can be met in Arctic field studies [28]. While the latter study illustrates the importance of adjusting for body size, such data are lacking in the older studies further emphasising the need for newer studies. Finally, while Greenland hosts a major Inuit population, data on BMC or BMD among Greenland Inuit is scarce. These limitations may be overcome by conducting new studies of bone quality among Inuit using updated techniques including the axial skeleton and a wider range of Inuit populations.

In conclusion, an overview of data on bone mineral content in Inuit is now available, depicted graphically and in tables for easy viewing and comparison. Findings among Inuit were similar across geography, age, and sex, and patterns were in keeping with findings among other populations. However, studies have methodological limitations with lack of adjustments for body size and living conditions and no assessment of bone structure. Hence, these results should be validated using modern techniques and adjustments before use in clinical practice. Thus, recent data is lacking, and data are warranted on the spine and hip. Such data could support validation of alternative fracture risk assessment methods for future clinical use among Arctic people.

Disclosure statement

No potential conflict of interest was reported by the author(s).