Certain groups are more prone to vitamin D deficiency, including: People who spend little time outdoors Those living in northern climates with long winters Individuals with darker skin tones (melanin reduces vitamin D synthesis) People who wear full-body coverings or sunscreen daily The elderly due to reduced skin synthesis and dietary intake Individuals with gut absorption disorders (e.g., celiac, Crohn’s disease) People with obesity, as vitamin D is sequestered in fat tissue Exclusively breastfed infants, especially if the mother is deficient Because vitamin D is stored in the body, deficiency can develop slowly over months or even years before symptoms become noticeable

Why the “Vitamin D” Is Essential for Your Body and Mind

You can’t see it, taste it, or feel it but your body depends on it every single day. Known as the “sunshine vitamin”, vitamin D plays a crucial role in everything from bone strength to immune defense and mental wellbeing. And yet, millions of people around the world are chronically deficient often without knowing it.

So, what makes this vitamin so important, how can you tell if you’re getting enough, and when should you consider supplementing?

What Is Vitamin D, and Why Does It Matter?

Vitamin D is a fat-soluble vitamin that your body produces naturally when your skin is exposed to sunlight, particularly UVB rays. It also exists in small amounts in certain foods and can be taken as a supplement.

Unlike most vitamins, vitamin D functions more like a hormone regulating calcium and phosphorus absorption, supporting muscle function, and helping modulate the immune system.

Key roles of vitamin D include:

Promoting strong bones and teeth
Supporting muscle strength and coordination
Boosting immune defenses against viruses and bacteria
Reducing inflammation
Supporting mood and cognitive function

A prolonged deficiency has been linked to conditions like osteoporosis, rickets in children, increased susceptibility to infections, and even symptoms of depression or fatigue.

Common Signs of Vitamin D Deficiency

Vitamin D deficiency can be silent or show up through vague, everyday symptoms. Some of the most common include:

Fatigue and low energy
Frequent illness or infections
Bone or muscle pain
Depressed mood or seasonal affective disorder (SAD)
Hair thinning
Slow wound healing
Loss of strength or frequent muscle cramps

Severe deficiency can lead to osteomalacia (bone softening) in adults or rickets in children, conditions that result in bone pain, deformities, and increased fracture risk.

Who’s at Risk?

Certain groups are more prone to vitamin D deficiency, including:

People who spend little time outdoors
Those living in northern climates with long winters
Individuals with darker skin tones (melanin reduces vitamin D synthesis)
People who wear full-body coverings or sunscreen daily
The elderly due to reduced skin synthesis and dietary intake
Individuals with gut absorption disorders (e.g., celiac, Crohn’s disease)
People with obesity, as vitamin D is sequestered in fat tissue
Exclusively breastfed infants, especially if the mother is deficient

Because vitamin D is stored in the body, deficiency can develop slowly over months or even years before symptoms become noticeable.

How Much Vitamin D Do You Need?

Recommended daily intake varies by age, location, and individual health factors. General guidelines suggest:

Infants (0–12 months): 400 IU (10 mcg)
Children and adults: 600–800 IU (15–20 mcg)
Older adults (70+): 800–1000 IU (20–25 mcg)
Pregnant or breastfeeding women: 600–800 IU (may vary by region)

However, some individuals especially those with deficiencies may need higher therapeutic doses, but only under medical supervision.

Blood levels of 25-hydroxyvitamin D (25(OH)D) are used to assess status. A level of 30–50 ng/mL (75–125 nmol/L) is generally considered optimal.

Natural Sources of Vitamin D

Sunlight is the most effective and natural source but only under the right conditions:

Aim for 10–30 minutes of midday sun, 2–3 times per week
Expose arms, legs, or face without sunscreen (briefly)
Be mindful of UV index and skin type

Food sources include:

Fatty fish (salmon, mackerel, sardines)
Cod liver oil
Egg yolks
Liver
Fortified dairy, cereals, or plant-based milks

Still, diet alone is rarely enough to maintain optimal levels especially in winter or in sun-limited lifestyles.

Should You Take a Supplement?

If you’re at risk of deficiency or your blood levels are low, supplementation is usually recommended. Vitamin D supplements come in two main forms:

Vitamin D2 (ergocalciferol) – plant-based, less potent
Vitamin D3 (cholecalciferol) – more effective at raising and maintaining blood levels

Always follow medical advice for dosing. While rare, too much vitamin D can lead to toxicity, causing calcium buildup in the blood (hypercalcemia), which may damage the kidneys or heart.

Vitamin D and Immune Health

Recent research has highlighted vitamin D’s role in reducing the severity of respiratory infections, including colds and flu. It helps modulate the immune response and reduce inflammation, which may explain why deficiency is more common in people with frequent infections.

This has renewed public interest in vitamin D as a supportive tool for immune resilience, especially during winter months.

A Small Vitamin With a Big Impact

Vitamin D might not grab headlines like other nutrients, but it quietly supports many of the body’s most critical systems, bones, immunity, mood, and more. And in today’s mostly indoor world, ensuring adequate levels is more important than ever.

If you suspect a deficiency, experience symptoms, or simply want to be proactive about your health, the internal medicine and endocrinology specialists at Erdem Hospital offer personalized testing, nutritional counseling, and treatment plans so you can feel strong, supported, and balanced, all year round.