Vitamin D

What is Vitamin D?

Vitamin D, often called the "sunshine vitamin," is a fat-soluble vitamin that plays a central role in the body's calcium balance, skeletal health, and immune defence. Unlike most other vitamins, the body can produce vitamin D itself — but only when the skin is exposed to UVB radiation from the sun.

Why is vitamin D important?

Vitamin D fulfils several vital functions in the body:

• Calcium absorption — Vitamin D is necessary for the intestine to absorb calcium from food. Without sufficient vitamin D, the body can only absorb 10-15% of the calcium you eat, compared to 30-40% at normal levels.
• Skeletal health — By regulating calcium and phosphorus levels, vitamin D helps build and maintain strong bones and teeth. Deficiency can lead to soft bones (osteomalacia) in adults and rickets in children.
• Immune defence — Vitamin D activates T cells and other immune cells needed to fight infections. Research shows that people with low vitamin D levels are more susceptible to colds and influenza.
• Muscle function — Vitamin D affects muscle strength and balance. Deficiency can lead to muscle weakness and increased risk of falls, especially in older adults.
• Mood and mental health — There are links between low vitamin D levels and depression, particularly the form known as seasonal affective disorder (SAD).

Vitamin D3 vs D2 — what is the difference?

There are two main forms of vitamin D:

• Vitamin D3 (cholecalciferol) — The form produced in the skin and found in animal foods. D3 is the most effective form and raises blood levels faster and longer.
• Vitamin D2 (ergocalciferol) — Derived from plants and fungi. Less effective than D3 but can be an option for vegans.

Most experts recommend vitamin D3 for optimal effect.

How much vitamin D do I need?

The recommended daily intake varies depending on age and life situation:

• Children 0-1 year: 400 IU (10 µg)
• Children and adults 1-70 years: 600-800 IU (15-20 µg)
• Adults over 70 years: 800-1000 IU (20-25 µg)
• Pregnant and breastfeeding women: 600-800 IU (15-20 µg)

Many researchers believe these recommendations are too low and that 1000-4000 IU daily may be more optimal, especially during the Swedish winter.

Vitamin D deficiency in Sweden

Sweden is located at a latitude where the sun's UVB radiation is too weak for vitamin D production from October to March. Studies show that up to 50% of the Swedish population have suboptimal vitamin D levels during winter. Risk groups include:

• People who spend little time outdoors
• Older adults with reduced skin synthesis
• People with darker skin tones
• Overweight individuals (vitamin D is stored in fat tissue)
• Vegans who do not take supplements

Good sources of vitamin D

Besides sunlight, vitamin D is found in:

• Fatty fish (salmon, mackerel, herring) — 400-1000 IU per serving
• Egg yolk — approx. 40 IU per egg
• Fortified foods (milk, margarine)
• Mushrooms exposed to UV light
• Dietary supplements — the safest way to achieve optimal levels

Can you overdose on vitamin D?

Vitamin D toxicity is rare but possible with very high doses (over 10,000 IU daily for a prolonged period). Symptoms include nausea, elevated blood calcium, and kidney problems. The upper limit is considered 4000 IU per day for adults, but short-term higher doses under medical supervision may be justified in confirmed deficiency.

Swedish recommendations (National Food Agency)

The National Food Agency recommends the following daily intake of vitamin D:

Source: National Food Agency, Nordic Nutrition Recommendations (NNR 2023). The National Food Agency recommends vitamin D supplementation from October to March for everyone in Sweden.