Mussel Intake and Vitamin D Status in Humans
Condition: Cardiovascular Disease
MeSH terms: Cardiovascular Diseases
Study type: Interventional

Summary: 
      A significant proportion of the United Kingdom population have inadequate levels of vitamin D
      in their blood. Vitamin D is a fat-soluble vitamin that is essential for the growth and
      maintenance of healthy bones through increasing dietary calcium absorption within the body. A
      low vitamin D status has also been associated with other diseases such as osteoporosis,
      cancer (especially colorectal cancer), cardiovascular disease and type 1 diabetes. Our skin
      is able to synthesise vitamin D upon exposure to sunlight in summer. If exposure to sunlight
      is limited, then a dietary supply of vitamin D becomes essential.

      However, very few foods contain vitamin D. Among the best dietary sources of vitamin D are
      oily fish (including salmon, mackerel, herring and trout) and fish oils. Recently, the
      investigators found that certain shellfish, especially mussels, contain significant amounts
      of a metabolite of vitamin D, 25(OH)D3. Consumption of this metabolite, as a supplement, has
      already been shown to improve vitamin D status in humans. Whether consumption of mussels
      improves vitamin D status is unknown.

      In this study the investigators will be looking at whether consumption of 1, 2 or 3 portions
      of mussels per week for 12 weeks increases vitamin D status in healthy people.
    

Detailed description: 
      Vitamin D, the main forms being vitamin D2 (ergocalciferol) and D3 (cholecalciferol), is a
      group of fat-soluble secosteroids which are synthesised from ergosterol in fungi and yeast,
      or from 7-dehydrocholesterol in humans, animals including fish and plants including
      microalgae, upon exposure to UV radiation. The metabolically inert vitamin D3 is then
      converted into 25-hydroxy D3 (25(OH)D3) and subsequently into 1α,25-dihydroxy D3
      (1,25(OH)2D3).

      A significant proportion of the global population have inadequate vitamin D levels - as
      defined by a plasma 25(OH)D concentration of <25 nM, - a level where the risk of poor
      musculoskeletal health appears to increase, which is especially apparent in older children,
      younger adults, older institutionalised individuals and infants from black and ethnic
      minority groups. Data from the NDNS and other studies suggest that between 29 and 54% of
      various population groups in the UK have a serum 25(OH)D concentration < 25 nmol/L in the
      winter. However, summer synthesis of vitamin D, facilitating maintenance of winter serum
      25(OH)D concentration ≥ 25 nmol/L is clearly not occurring for many in the UK population
      (Consultation on draft SACN Vitamin D and Health report). If there is inadequate vitamin D3
      synthesis within the skin, generally caused by limited exposure to sunlight, then a dietary
      supply of vitamin D becomes essential.

      Overall however, very few foods contain vitamin D. Among the best dietary sources of vitamin
      D are oily fish (including salmon, mackerel, herring and trout) and fish oils, providing up
      to 20g of vitamin D per 100 g. Lower amounts of vitamin D are present in red meat, liver and
      egg yolks (approximately 1-5g/100 g). Vitamin D in these foods and in fish is primarily in
      the form of vitamin D3 and its metabolite 25(OH)D3.

      Recently, investigators have found that certain shellfish, especially mussels, contain
      significant amounts of 25(OH)D3, ranging from 0.7 to 9.9 µg/100 g wet weight. Thus far, food
      composition databases give either very low or no values for levels of vitamin D in shellfish.
      The amount of vitamin D3 in mussels is either reported to be below the detection limit, or is
      not analysed, in mussels in the food database analysis. The importance of finding 25(OH)D3
      rather than vitamin D3 in mussels is illustrated by the fact that this metabolite is
      considered 5 times more effective in raising serum 25(OH)D3 levels in humans, and thus
      vitamin D status, than vitamin D3 itself. An interesting parallel with meat appears. Meat
      contains little native vitamin D but as better measurement techniques detected more
      metabolites of vitamin D, which were considered to be more potent, these have been added to
      food composition tables. Indeed, the apparent increase in vitamin D intakes in the British
      household food data, in 1995 and 1996, is a direct result of including the potency factor for
      meat. Taking account of this potency factor, mussels could provide up to 50g of vitamin D per
      100g. Whether consumption of mussels improves vitamin D status in humans is however, not
      known.

      According to exploratory meta-regression analyses of RCT data in a number of European
      (51-60°N) winter-based, dose-related RCTs which used supplemental doses of vitamin D between
      0-20 μg/d, have reported vitamin D-serum 25(OH)D concentration slope estimates of 1.55-2.43
      nmol/L increment per 1 μg vitamin D (Consultation on draft SACN Vitamin D and Health report).
      Thus 1, 2 and 3 portions of mussels per week, providing the equivalent of approx. 2.7, 5.4
      and 8.0 mg/day (including the potency factor of 5) may increase serum levels of 25(OH)D3 by
      4.2-6.6 nmol/L for 1 portion of mussels per week, 8.4-13.1 nmol/L for 2 portions per week or
      12.4-19.4 nmol/L for 3 portions of mussels per week
    

Intervention name(s): No Mussels; One mussel portion; Two mussel portions; Three mussel portions
Intervention type(s): Dietary Supplement; Dietary Supplement; Dietary Supplement; Dietary Supplement
Intervention description(s): Habitual diet only; 1 x 75g mussel portions provided per week; 2 x 75g mussel portions provided per week; 3 x 75g mussel portions provided per week
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Investigator)
Primary purpose: Prevention
Keywords: Mussels; Dietary Intervention; Long-term intervention; Vitamin D status; Selenium; Iodine; Vitamin B12; Omega-3 index