Although vitamin D is important and essential for health, certain groups of people need to be cautious when supplementing this nutrient.

Vitamin D is not actually a vitamin but a fat-soluble pro-hormone. There are two forms of vitamin D: Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Both are converted in the body to the active form of vitamin D.

Vitamin D2 is naturally synthesized by plants, while vitamin D3 is produced by the body when the skin is exposed to ultraviolet rays (primarily UVB) from the sun.

Under the influence of ultraviolet rays from sunlight, the skin produces cholecalciferol. This substance is then transported and metabolized in the liver into 25-hydroxycholecalciferol (25(OH) vitamin D), and subsequently converted in the kidneys to its active form, 1,25-dihydroxycholecalciferol, which is the metabolite with active vitamin D.

This production process varies greatly depending on geographic location, season, time of day, and even skin pigmentation. Both vitamin D2 and D3 can be chemically produced and used as supplements.

The doctor will recommend vitamin D supplementation based on blood test results to determine if there is a deficiency of this nutrient.

1. The Role of Vitamin D

The main function of vitamin D is to ensure sufficient levels of calcium and phosphorus in the blood, helping the intestines absorb these minerals and reducing their excretion through the kidneys.

This support allows for:

• Optimal mineralization of bones, cartilage, and teeth
• Regulation of muscle function
• Enhanced nervous system activity
• Normal blood clotting

Additionally, vitamin D is involved in hormonal balance and contributes to the immune system’s functioning. Due to its role in the accurate functioning of immune cells, a deficiency in vitamin D may be linked to an increased risk of infections such as colds and flu.

2. Who is at Risk of Vitamin D Deficiency?

Certain populations at risk for vitamin D deficiency include: infants, young children, pregnant women, and the elderly. The ability to absorb or synthesize vitamin D declines with age. In older adults, low vitamin D levels can lead to bone loss and consequently osteoporosis.

Other factors that may exacerbate these deficiency risks include skin pigmentation, specific dietary restrictions (such as eliminating meat, fish, eggs, and dairy products), and medical conditions that cause malabsorption in the intestines.

Clinical signs of vitamin D deficiency include:

• Osteomalacia and rickets
• Muscle weakness
• Seizures (related to hypocalcemia) and sometimes anemia.

For individuals at risk of deficiency, blood tests should be conducted to measure serum levels of 25(OH) vitamin D. The levels should ideally fall between 30 and 45 ng/ml. If vitamin D levels are below 30 ng/ml, a doctor may recommend supplementation to restore normal levels.

It’s important to avoid the mindset of “the more, the better” when it comes to vitamin D supplementation. Excessive vitamin D (doses > 10,000 IU/day) can occur with over-supplementation and may cause dehydration, nausea, weight loss, and even kidney failure.

3. Caution When Supplementing Vitamin D

While vitamin D is an important nutrient for health, certain groups need to be cautious.

These groups include:

• People with Kidney Issues: Individuals with kidney function problems, such as kidney failure, may experience vitamin D accumulation in the body, putting additional strain on the kidneys to filter the blood.
• Kidney Stones: Increased vitamin D levels can raise calcium in urine, potentially contributing to the formation of certain types of kidney stones.
• Individuals with Allergic Reactions to Vitamin D: Some people may experience allergic reactions or side effects from using vitamin D, including diarrhea, nausea, fatigue, or dizziness. If any unusual or abnormal signs occur after supplementation, usage should be discontinued, and a doctor should be consulted.
• Those Consuming High Amounts of Vitamin D: If consuming large amounts of vitamin D from rich dietary sources such as fatty fish, supplements, and fortified products, it may be wise to reduce intake from other sources.
• Pregnant or Breastfeeding Women: Pregnant or breastfeeding women should be cautious with vitamin D supplementation, as nutritional needs during this period can differ. Discuss appropriate dosages with a doctor.

Before supplementing with any vitamin, it is advisable to consult a doctor or nutritionist, especially if you belong to groups that should be cautious about using vitamin D. A healthcare provider can evaluate your health status and recommend appropriate vitamin D supplementation.