Does the fish have a good vitamin D status?

Vitamin D is best known for its role in regulating calcium and phosphorus metabolism. However, research over the past two decades has demonstrated that vitamin D also plays a central role in both the innate and adaptive immune systems. Among its many functions, vitamin D is essential for regulating tight junction proteins that maintain the barrier integrity of the body's internal and external surfaces, including the skin, intestine, and gills. Consequently, suboptimal vitamin D status can be expected to affect robustness, wound healing, and susceptibility to infections.

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Vitamin D in fish – nutritional value vs. fish health

Measuring vitamin D concentrations in fillet (or whole fish) is important for documenting the nutritional value of fish intended for human consumption.

 

For fish health, however, the circulating concentrations of vitamin D metabolites in plasma are the key indicators. Experience from human nutrition has shown that large vitamin D stores in adipose tissue do not necessarily protect against vitamin D deficiency. Individuals with obesity may have substantial amounts of vitamin D stored in adipose tissue while simultaneously exhibiting low circulating vitamin D levels and the clinical signs of vitamin D deficiency. Vitamin D stored in adipose tissue is predominantly present as fatty acid esters and therefore does not constitute a readily available functional reserve. Mobilization back into the circulation occurs only during significant weight loss or prolonged, intense physical activity.

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New and surprising findings in farmed atlantic salmon

In our recently published study, we present field-based evidence demonstrating that Atlantic salmon can synthesize vitamin D in response to natural sunlight. Salmon reared in open sea cages exhibited significantly higher circulating concentrations of vitamin D metabolites than fish raised indoors, despite receiving the same commercial diet.

 

The differences were both substantial and unexpected. Plasma concentrations of vitamin D3 and 25(OH)D3 were several-fold higher in outdoor-reared fish and followed a clear seasonal pattern, with low levels during winter and high levels during summer. When fish were transferred from indoor production systems to outdoor conditions, circulating vitamin D concentrations increased rapidly. In a controlled experiment, whole-fish vitamin D stores increased five-fold after only 52 days of daylight exposure.

 

These findings indicate that fish reared indoors, or produced during periods with limited natural daylight, are likely to have an increased risk of suboptimal circulating vitamin D concentrations, even when tissue vitamin D levels remain relatively high

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Which vitamin D metabolites should be measured?

To assess the metabolic vitamin D status of fish, we recommend measuring the circulating plasma concentrations of both vitamin D3 and 25(OH)D3. Recent human research has demonstrated that many peripheral tissues possess the enzymes required for local activation of vitamin D, including direct activation from vitamin D3.

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To assess the nutritional value of fish for human consumption, we recommend measuring vitamin D3 and 25(OH)D3 in fillet or whole fish.

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FishLab's Validated LC-MS/MS Methods for Vitamin D Analysis:

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Plasma

• Vitamin D3

• 25(OH)D3

• 1,25(OH)2D3

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Tissue analyses (Fillet, Liver, and Whole Fish)

• Vitamin D3

• 25(OH)D3

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