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Obese people have lower vitamin D because they are bigger

2014-05-20

May 20, 2014, Prague, Czech Republic. Press Dispensary. It may seem self-evident that if obese people have lower blood levels of vitamin D – as has been found to be the case, among different ethnicities and countries – it will probably be because a bigger body means there is a greater volume through which it has to be distributed. But size need not necessarily be the cause: lower levels could also be due to other factors, such as lower binding proteins, lower dietary intake, lower sunlight exposure or more rapid metabolic clearance. So a recent study has set out to see whether the 'greater volume of distribution' is indeed the cause.

The outcome was presented today by Jennifer Walsh of the University of Sheffield, speaking at the 41st European Calcified Tissue Society Congress, held in Prague, May 17-20, 2014.  Dr Walsh described how a seasonal study of 216 adults sought to determine if free 25OHD and total 1,25(OH)2D (1,25-dihydroxyvitamin D) are also lower in obese people, along with total 25OHD, while the other factors remain constant.

Dr Walsh explained: "Our 216 adult participants were categorised into three weight groups: normal weight, overweight and obese. In autumn and spring we assessed them by measuring their vitamin D and providing questionnaires to determine their exposure to sunlight and their intake of dietary vitamin D. And in winter, we assessed the metabolic clearance of 25OHD in 112 of the participants by measuring the half-life of an orally administered stable isotope."

The data gathered were all adjusted for date of sample collection, age group and gender.

Dr Walsh continued: "In autumn and spring, the total 25OHD, free 25OHD and total 1,25(OH)2D were all lower in the obese people: the greater the BMI, the lower these were. And the difference in 25OHD between normal weight and obese groups was greater in autumn and spring than in winter. However, there was no difference between the three groups in dietary vitamin D, sunlight exposure and 25OHD half-life, eliminating those as a possible cause.

"Circulating vitamin D is lower in obesity and we conclude that this is likely to be due to greater volume of distribution for vitamin D. Obese people have lower vitamin D because they have larger body size."

This study is independent research commissioned and funded by the Department of Health Policy Research Programme (The Value of 25 Hydroxyvitamin D as a Biomarker in Obesity, 024/0052). The views expressed are those of the authors and not necessarily those of the Department of Health.

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Notes for editors
The European Calcified Tissue Society (ECTS) is the major organisation in Europe for researchers and clinicians working in the field of calcified tissues and related fields. ECTS acts as a forum for the dissemination of high quality research through its annual meeting, the European Symposium on Calcified Tissues, and through training courses and workshops.

Calcified tissues are central to a healthy skeleton and to bone disorders - such as osteoporosis, back pain and fractures - that make life a misery for countless people. Children can inherit some forms of bone diseases causing bone pain, shortness and deformed limbs.

The 41st European Calcified Tissue Society Congress is taking place in Prague, the Czech Republic, on May 17-20, 2014.

The ECTS Annual Congress gives delegates the opportunity to collaborate with leading international researchers and clinical colleagues. Main discussion points are the latest in high quality science and research to benefit clinical practice.

ECTS 2015 will be in Rotterdam, 25-18 April 2015.

About the study

The aims of the study - conducted by teams from the Academic Unit of Bone Metabolism, University of Sheffield and Sheffield Teaching Hospitals, the School of Health and Related Research, University of Sheffield and the Cambridge MRC Human Nutrition Research Unit – were to determine if free 25OHD and 1,25-dihydroxyvitamin D (1,25(OH)2D) are also low in obese people, along with the already known behaviour of total 25OHD, indicating the cause of low vitamin D in obesity.

The study assessed 216 normal weight (BMI 18.5-25), overweight (BMI 25-30) and obese (BMI >30) adults ages 25-40 and 55-75 in autumn/spring, with vitamin D measurements and questionnaires for sunlight exposure and dietary vitamin D. Metabolic clearance of 25OHD was assessed by half-life of an orally administered stable isotope in 112 participants in winter.

In autumn/spring, total 25OHD (immunoassay and LC-MS/MS), free 25OHD (measured and calculated) and total 1,25(OH)2D (all adjusted for date of sample collection, age group and gender) were lower in obese people (ANCOVA p<0.002), and negatively correlated with BMI (R2 total 25OHD 0.248; free 25OHD 0.296; 1,25(OH)2D 0.055, all p<0.05). The difference in 25OHD between normal weight and obese groups was greater in autumn/spring than in winter. Dietary vitamin D, sunlight exposure and 25OHD half-life did not differ by BMI group.

The conclusion was that total and free 25OHD and 1,25(OH)2D are lower in obesity and this is likely to be due to greater volume of distribution for vitamin D.

Total 25OHD, nmol/lFree 25OHD, pmol/lTotal 1,25(OH)2D, pmol/l
Normal
N=75
53.6
(46.7, 61.4)
10.63
(9.43, 11.98)
95.0
(87.1, 103.7)
Overweight
N=61
40.6
(35.4, 46.6)
7.49
(6.54, 8.59)
79.4
(72.3, 87.1)
Obese
N=80
38.5
(34.0, 43.7)
7.79
(6.91, 8.76)
78.5
(72.3, 85.3)
Measurements by immunoassay in autumn/spring
Geometric mean (95% CI), ANCOVA group differences all p0.002

For further information, please contact:
Roberta Mugnai, ECTS executive director
European Calcified Tissue Society (ECTS)
Tel: + 32 476 520 716
Email:
Site: www.ectsoc.org

Congress site: www.ectscongress.org/2014/
Twitter: @ECTS_soc
Hashtag: #ECTS14

Media contacts

Roberta Mugnai, ECTS executive director
Tel: + 32 476 520 716
Email:
Site: www.ectsoc.org

Congress site: www.ectscongress.org/2014/
Twitter: @ECTS_soc
Hashtag: #ECTS14

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