Estimation of the Dietary Requirement for Vitamin D in Ethnic Groups

Estimation of the Dietary Requirement for Vitamin D in Ethnic Groups: a Double-blind, Randomised, Dose-response Trial

The aim of this study is to perform a double-blind, randomised, dose-response trial of vitamin D3 supplementation in United Kingdom (UK)-dwelling adults of white European, South Asian, and black African/Caribbean ethnicity to investigate the distribution of dietary intakes needed to maintain adequate vitamin D status in winter, as indicated by serum 25(OH)D concentrations at ranges of >25 to 50 nmol/L. In addition, this study will investigate the effect of vitamin D3 supplementation on immune health, muscular strength, and overall health.

The aim of this study is to perform a double-blind, randomised, dose-response trial of vitamin D3 supplementation in United Kingdom (UK)-dwelling adults of white European, South Asian, and black African/Caribbean ethnicity to investigate the distribution of dietary intakes needed to maintain adequate vitamin D status in winter, as indicated by serum 25(OH)D concentrations at ranges of >25 to 50 nmol/L. In addition, this study will investigate the effect of vitamin D3 supplementation on immune health, muscular strength, and overall health. Recruited participants will be randomised to take 400, 1000, or 2000 IU for 12 weeks. Fasting blood samples collected at baseline and 12 weeks will measure biochemical markers of vitamin D status (serum 25(OH)D, calcium, parathyroid hormone, albumin), lipid profile, ferritin, micronutrient status, and immune and inflammatory biomarkers. Muscular strength will be measured using sit-to-stand and grip strength tests. Questionnaires, food diaries, and dosimeters will be used to gather data on lifestyle, physical activity, dietary intake, and sun exposure.

A blood sample will be analysed using liquid chromatography tandem mass spectroscopy (LC-MS). Dose-response change in serum 25(OH)D will be measured in nmol/L.

Muscular strength measured using a dynamometer (measured to the nearest 0.1kg). The participant will squeeze the dynamometer with maximum effort for 5 seconds.

Vitamin D intake will be measured through a 4-day food diary which participants will fill out for 4 day at home before and after the study.

Assess level of physical activity using an International Physical Activity Questionnaire (short form)

Measures amount of time spent in the sun (often, occasionally, never) and what parts of the body are exposed (head, hands, arms, legs, torso) over summer, spring, autumn and winter. Also questions any summer holidays abroad, in what month, what country was visited, number of hours of sun per day and what body parts were exposed (head, hands, arms, legs, torso)

Sun exposure will be measured by a dosimeter, which measures UVB exposure. Participants wear this like a badge for 4 days before and after the study.

Measures: - Skin type (Fitzpatrick scale) Questions: Questions what ethnicity they identify with, Holidays abroad, Education, Origin, Health, Pregnancy, Sun behaviours (what body parts are usually exposed to the sun, clothing, sun bathing, sunscreen use, sun bed use), Smoking, Drinking, Recreational drug use, Knowledge around vitamin D, supplement use, Milk, egg, oily fish and liver consumption

Inclusion Criteria: British white European, black African/Caribbean, or South Asian (self-reported) Living in England for >2 months Aged >18 years No significant health issues English or Urdu speaker Exclusion Criteria: Medical condition or history which might impact study measurements (e.g., ischaemic heart disease, type 1 and type 2 diabetes, thyroid disease, osteoporosis, haematological disease, malignancy) Medications known to affect vitamin D metabolism (i.e., hormone replacement therapy, anti-oestrogens treatment, antiepileptic drugs, and breast cancer treatment) Pregnant or planning pregnancy during the study period Regular use of sun beds Having a sun holiday one month prior to commencing study or plans for a sun holiday within the study period. A sun holiday is generally defined as a holiday in a sunny resort outside of the UK. The researchers will assess this on a case-by-case basis depending on the time of year and expected weather conditions Reported participation in another clinical trial occurring simultaneously Previous intolerance or allergic reaction to vitamin D