Best Practice & Research Clinical Endocrinology & Metabolism
12Worldwide vitamin D status
Introduction
Vitamin D status has been studied in all continents and most countries over the world. Several reviews have been published.1, 2, 3, 4, 5, *6, 7, *8 The best determinant of vitamin D status is the serum concentration of 25-hydroxyvitamin D (25(OH)D).1 There is no general agreement on the required serum 25(OH)D for an adequate vitamin D status. Most investigators agree that serum 25(OH)D should be higher than 50 nmol/l, but some recommend higher serum levels, e.g. higher than 75 or even 100 nmol/l.9 The Institute of Medicine has recently recommended that serum 25(OH)D is adequate when it is higher than 50 nmol/l,10 similar to the recommendation of the Standing Committee of Europe Doctors (www.cpme.eu). Clinical vitamin D deficiency only occurs when serum 25(OH)D is lower than 25 nmol/l. The clinical picture includes muscle weakness, bone pain and fractures, while in children joint swelling and deformations prevail. In patients with rickets and osteomalacia serum 25(OH)D usually is lower than 15 nmol/l or even below the detection limit.11 The variation in serum 25(OH)D measurements is still considerable due to laboratory variation.12 Different radio-immunoassays yield different results and the variation between laboratories may be as high as 30%. New methods such as liquid chromatography followed by mass spectrometry give better results.13 Vitamin D status is determined by sunshine exposure, skin pigmentation, clothing style, use of sunscreen, nutrition and supplements. A small part of the serum 25(OH)D comes from dietary intake, especially fatty fish. The dietary intake is more important when sunshine exposure is less. In the next paragraphs vitamin D status is described in different continents and different countries. The emphasis is on vitamin D status in adults. Attention will also be focussed on determinants of vitamin D status and on risk groups for vitamin D deficiency. This chapter will end with a research agenda.
Section snippets
Europe
Vitamin D status in Europe varies according to latitude, season and skin pigmentation. The serum 25(OH)D level as observed in different studies14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28 is shown in Fig. 1. As visible in this Figure, serum 25(OH)D is higher in Northern Europe than in Southern Europe and higher in Western than in Eastern Europe. The higher levels in Northern Europe were also observed in some multicenter studies in which one laboratory facility was used.1, *6, *8,
Middle-East
The mean serum 25(OH)D levels in various countries of the Middle-East are shown in Fig. 2. Serum 25(OH)D shows a high variation in these countries.30, 31, 32, 33, 34, *35, 36 In a population study of 1210 men and women in Iran between 20 and 69 years the mean serum 25(OH)D was 20.6 nmol/l.35 Vitamin D status was better in girls and boys between 14 and 18 years (mean 42 and 92 nmol/l, respectively).36 The lowest serum 25(OH)D was seen in a study of older persons in Saudi Arabia with a mean of
Africa
Studies from Africa37, 38, 39, 40, 41, 42, 43 show in general adequate or even high mean serum 25(OH)D levels (Fig. 3). Population-based data are not available. The studies from Tanzania and Guinea-Bissau showed a serum 25(OH)D of 87 and 78 respectively in tuberculosis patients.40, 42 In a study in Gambian rural women, serum 25(OH)D was 91 nmol/l.37 A lower serum 25(OH)D was measured in Tunesia with a mean level of 35 nmol/l in veiled and 43 nmol/l in non-veiled women.43
Asia
The mean serum 25(OH)D levels in different studies from Asia are shown in Fig. 444, 45, 46, 47, 48, 49, 50, 51, 52 A low serum 25(OH)D was observed in hip fracture patients and controls of similar age in a study in Yekaterinburg in Asian Russia.44 Low serum 25(OH)D levels were also observed in Mongolia with a very low level in rachitic children (7 nmol/l) and pregnant women (26 nmol/l).45 In a population study in Chinese girls of 12–15 years very low levels were found in winter (12–13 nmol/l).45
Oceania
The mean serum 25(OH)D levels in different studies from Oceania, i.e. Australia, New Zealand and Pacific Islands, are shown in Fig. 5.*53, 54, 55, 56, 57, 58, 59 Although Oceania has a very sunny climate, mean 25(OH)D levels were below 50 nmol/l (39.7 nmol/l in low-level care and 31.4 nmol/l in high-level care) in a large sample of women in residential care in three states of Australia (Western Australia, New South Wales, Victoria).53 In individuals aged 60 years and older, mean 25(OH)D levels
North-America (including Canada and Mexico)
Many studies examining the vitamin D status in North-America were published (Fig. 6,60, 61, 62, 63, 64, 65, *66, *67, *68), among which several representative samples of the US population. One of the largest representative samples available is The National Health and Nutrition Examination Survey (NHANES). The most recent NHANES data on vitamin D status are from 2005–2006. The mean serum 25(OH)D level in 4495 individuals was 49.8 nmol/l; 50.3 nmol/l in men and 49.5 nmol/l in women.67
South-America
Only few studies on vitamin D status in South-America were published (Fig. 7,*69, 70, 71, 72). Most of these studies were small, and data from several countries are lacking. In a study in Argentina, a clear North-South gradient was observed with higher vitamin D levels near the equator.69 In Chile, lower 25(OH)D levels were observed in postmenopausal as compared with premenopausal women.71 The observed mean level in postmenopausal women in Chile (48.8 nmol/l) is very similar to the mean 25(OH)D
Risk groups
This chapter shows that serum 25(OH)D levels are suboptimal in adults in many countries. Vitamin D deficiency is even more common in specific risk groups. Vitamin D deficiency is prevalent in pregnant women and their newborns.46, 73, 74, 75 The highest risk was observed in black women and their newborns. Low vitamin D levels were also reported in children,76 esp. obese children,77 and in adolescents.5 Low vitamin D status in children and adolescents may be due to reduced intake or synthesis of
Conclusion
Vitamin D deficiency has a high prevalence over the world, not only in risk groups. Especially, in the Middle-East and Asia, vitamin D deficiency in adults is highly prevalent. Traditional risk groups include young children, pregnant women, older persons, the institutionalized, and non-western immigrants. Recent studies show that adolescents and young adults are at risk for vitamin D deficiency. Risk factors for vitamin D deficiency include low sun exposure, skin pigmentation, sunscreen use,
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