Vitamin D deficiency: when levels are very low

Vitamin D deficiency is a disorder characterized by low levels of this vitamin in the blood.

Vitamin D has multiple functions, some of which are as follows:

• Regulates calcium and phosphate levels at the renal level: it promotes calcium absorption in the intestines from food and its reabsorption in the kidneys to reduce losses through urine
• Supports bone mineralization and remodeling: vitamin D plays a fundamental role in bone formation and skeletal development
• Promotes muscle volume increase: thus, it plays a key role in skeletal muscle development
• Inhibits the secretion of parathyroid hormone (PTH): PTH promotes the release of calcium from bones
• Modulates the immune system: it helps transform monocytes into macrophages

Vitamin D itself is biologically inactive and requires a series of chemical transformations to perform its functions. First, in the skin, vitamin D is converted to cholecalciferol by ultraviolet rays from the Sun. Then, cholecalciferol is hydroxylated in the liver to form calcidiol. Finally, calcidiol is converted to calcitriol in the kidneys. Calcitriol is the biologically active form of vitamin D and is responsible for performing the aforementioned functions.

There are multiple causes of vitamin D deficiency, the most common of which are:

• Inadequate intake of vitamin D from the diet
• Inadequate or insufficient exposure to sunlight
• Problems with the absorption of vitamin D in the intestines
• Renal and/or hepatic disorders that interfere with its conversion to calcitriol
• Hypoparathyroidism
• Use of medications that interfere with the absorption of vitamin D and its conversion to calcitriol

Vitamin D deficiency can cause the following symptoms:

• Muscle pain
• Weakness and bone pain
• Muscle cramps (tetany)
• Rickets (in more severe cases)
• Bone density loss and osteoporosis

The main risk factors for vitamin D deficiency are:

• Age: in older adults, the skin produces less vitamin D, and the kidneys are less capable of converting it to calcitriol
• People with dark skin: they have a reduced ability to produce vitamin D from sunlight
• People with conditions that hinder nutrient absorption: such as Crohn's disease, ulcerative colitis, and celiac disease
• Obese individuals: their body fat binds some vitamin D, preventing it from entering the bloodstream
• People who have undergone gastric bypass surgery: a type of weight-loss surgery that creates a direct route to the small intestine, making it more difficult to absorb enough vitamin D, as it is absorbed there
• People with chronic kidney or liver disease: these conditions can affect the body's ability to convert vitamin D into a usable form
• People taking medications that affect vitamin D levels: including certain cholesterol medications, anticonvulsants, corticosteroids, and weight-loss medications

Vitamin D deficiency is diagnosed through a blood test. Vitamin D insufficiency is diagnosed if blood levels are between 20 and 30 ng/mL. On the other hand, vitamin D deficiency is diagnosed if blood levels are below 20 ng/mL.

Vitamin D deficiency can be treated by taking supplements to correct blood levels. Additionally, dietary changes can increase the intake of vitamin D-rich foods, ensuring the diet remains balanced and varied. Some foods rich in vitamin D include:

• Fatty fish (such as salmon, tuna, or mackerel)
• Cheese
• Egg yolks
• Soy beverages

Vitamin D is also commonly present in multivitamin supplements.

The best way to prevent vitamin D deficiency is by following a rich and balanced diet that includes frequent consumption of vitamin D-rich foods. Sun exposure also helps prevent vitamin D deficiency, as it plays a key role in converting vitamin D to calcitriol.