Vitamin D insufficiency: when levels are below normality

Vitamin D insufficiency is a metabolic disorder characterized by low levels of vitamin D in blood, but superior to levels considered as vitamin D deficiency.

Vitamin D performs multiple functions, including:

• Regulating calcium and phosphate levels: it promotes calcium absorption in the intestines from food and enhances its reabsorption in the kidneys, reducing calcium loss through urine
• Supporting bone mineralization and remodeling: vitamin D plays a crucial role in bone formation and skeletal development
• Increasing muscle mass: it contributes significantly to the development of skeletal muscle
• Inhibiting parathyroid hormone (PTH) secretion: PTH encourages calcium release from bones, and vitamin D helps regulate this process
• Modulating the immune system: vitamin D aids in transforming monocytes into macrophages

Vitamin D itself is biologically inactive and must undergo a series of chemical transformations to perform its functions. Firstly, in the skin, vitamin D is converted to cholecalciferol by ultraviolet rays from sunlight. Followed up by the liver, cholecalciferol is hydroxylated to form calcidiol. Lastly in the kidneys, calcidiol is converted into calcitriol, the biologically active form of vitamin D, responsible for its key functions.

The primary risk factors for vitamin D insufficiency include:

• Age: older adults produce less vitamin D in the skin, and their kidneys are less efficient at converting it to calcitriol
• Darker skin: melanin reduces the skin’s ability to produce vitamin D from sunlight
• Malabsorption conditions: diseases like Crohn’s disease, ulcerative colitis, and celiac disease can hinder nutrient absorption
• Obesity: body fat sequesters vitamin D, preventing it from entering the bloodstream effectively
• Gastric bypass surgery: this weight-loss procedure bypasses the small intestine, where vitamin D is absorbed, making it harder to obtain sufficient levels
• Chronic kidney or liver disease: these conditions impair the body’s ability to convert vitamin D into its usable form
• Certain medications: drugs such as cholesterol-lowering agents, anticonvulsants, corticosteroids, and weight-loss medications can affect vitamin D levels

Vitamin D insufficiency is diagnosed through blood tests. Insufficiency, Blood levels between 20 and 30 ng/mL. On the other hand, dficiency, blood levels below 20 ng/mL.

Vitamin D insufficiency can be treated with supplements to restore blood levels. Dietary adjustments can also help by increasing the intake of vitamin D-rich foods, ensuring the diet remains balanced and varied. Foods rich in vitamin D include:

• Fatty fish (e.g., salmon, tuna, and mackerel)
• Cheese
• Egg yolks
• Soy beverages

Vitamin D is also commonly included in multivitamin supplements.

The best ways to prevent vitamin D insufficiency is maintaining a rich and balanced diet with frequent consumption of vitamin D-rich foods and regular sun exposure, as it plays a key role in converting vitamin D into calcitriol.