There is a paucity of longitudinal data investigating the role of vitamin D in the maintenance of health in ethnic minority groups. Specifically, little is known about the role of vitamin D on muscle strength, how this affected by emigrating from low to high latitudes. This PhD thesis provides insight into the relationship between vitamin D status and muscle strength in healthy adults migrating from sunny climates (45°N to 45°S to the equator) to higher latitude (Aberdeen, 57°N) (first study) and also sunlight behaviours in both low and high latitudes (second study). A total of 71 people of ethnic minority aged 19-42 years took part in the first study with 56% were seen within 3 months of arriving in Aberdeen (newcomers) and the remainder having been resident for any longer period than this (residents). Participants attended visits every 3 months for 15 months. At each visit, fasted blood samples were collected for analysis of serum 25-hydroxyvitamin D [25(OH)D] by dual tandem-mass spectrometry, parathyroid hormone (PTH), carboxy-terminal collagen crosslinks (CTX) and N-terminal propeptide of type I collagen (P1NP) by electrochemiluminescent immunoassay. Maximal voluntary contraction (MVC) was measured using a Takei digital grip dynamometer (both arms) and a Biodex dynamometer (right knee) for isometric knee extension and isokinetic knee extension and flexion. Mean baseline 25(OH)D concentrations were higher in the newcomers (35.2 nmol/L) than the residents (25.0 nmol/L, p<0.01). After adjusting for the season of measurement at baseline, there was a trend for higher vitamin D status only between newcomers arriving in spring (33.5 nmol/L) and residents (26.8 nmol/L, p=0.09), but not between the newcomers arriving in autumn (36.1 nmol/L) and residents in autumn (35.2 nmol/L, p=0.81). Notably, few newcomers (13%) and residents (7%) had 25OHD concentrations >50 nmol/L. There was a small seasonal variation in 25(OH)D concentration with the difference between zenith (summer/autumn) and nadir (winter/spring) was 5 nmol/L, 6 nmol/L, and 12 nmol/L among the newcomers arriving in spring, autumn and residents, respectively. There was no seasonal variation in bone turnover markers. There was a positive, albeit small, association between vitamin D and knee extensor isometric torque. Mixed modelling predicted that each 1 nmol/L increase in 25(OH)D would increase peak torque by 1 Nm (p=0.04). If extrapolated to higher 25(OH)D, the change in muscle strength would be clinically meaningful. In the second study, 117 Asians in Kuala Lumpur (3°N) and 110 non-Europeans (78% Asians) in Aberdeen were recruited and monitored for one year [every 3 months for participants in Aberdeen and during Southwest monsoon (SWM; July-Sept) and Northeast monsoon (NEM; Nov-Feb) in Kuala Lumpur]. Personal sunlight exposures were assessed by polysulphone film badges and a web-based questionnaire. Asians living in their usual environment (Kuala Lumpur) had similar sunlight behaviours to Asians living in Aberdeen. Sunlight was the major source of vitamin D in Kuala Lumpur during both seasons (median % cutaneous in SWM = 61%; NEM = 59%), but only during summer in Aberdeen (52%). Dietary intakes provided the most source of vitamin D in Aberdeen during autumn (94%), winter (97%) and spring (56%). This thesis has added evidence to the current limited observations on vitamin D and muscle strength, particularly in the cohort of young adults migrating from low to high latitudes. Intervention studies are yet to be conducted with a speculation that an increase in vitamin D status may show a positive impact on muscle strength. The extent of low sunlight behaviour among healthy adults in Kuala Lumpur is of concern.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:680998 |
| Date | January 2016 |
| Creators | Jamil, Nor Aini |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=228979 |
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