Vitamin D and aging: what does the research say about optimal levels, supplementation and myths?

Why vitamin D is particularly relevant in Denmark

Denmark's northern location means that the UVB radiation from the sun is too weak to form vitamin D in the skin from around October to March. It is a physiological reality, not an attitude. During that period, the body is dependent on depots and diet. PMID 32744000 PMID 28496129

At the same time, fatty fish, eggs and fortified dairy products are the primary dietary sources, but many Danes do not get enough through diet alone. The combination of dark winters, a lot of indoor life and limited dietary sources make vitamin D one of the most relevant micronutrients in Danish prevention. PMID 32744000 PMID 28496129

For older adults, the situation is often more pronounced because the skin's ability to produce vitamin D declines with age and because mobility and outdoor time are often reduced. PMID 32744000 PMID 28496129

What vitamin D actually does in the body

Vitamin D acts as a steroid hormone that regulates hundreds of genes. The classic role is calcium and phosphate balance, which is essential for bone mineralization. But vitamin D also affects the immune system, muscle cells, insulin secretion and cell division. PMID 28496129 PMID 23853635

However, it is important to distinguish between association and causality. Many observational studies show that low vitamin D is associated with higher mortality, more infections and poorer cognitive function. But intervention studies where vitamin D is given to people without a proven deficiency have often shown weaker or absent effects. This suggests that vitamin D is primarily important when there is actually a deficiency, but does not necessarily provide additional benefit at already sufficient levels. PMID 28496129 PMID 23853635

Optimal levels and when a supplement makes sense

Serum 25(OH)D is the best marker of vitamin D status. Most Danish and international guidelines define levels below 25-30 nmol/L as deficiency, 30-50 nmol/L as insufficient, and 50-75 nmol/L or higher as sufficient for most. Some researchers argue for higher targets (75-120 nmol/L), but the evidence for additional benefit above 75 nmol/L is weak for most healthy adults. PMID 23853635 PMID 22356356

The question of routine screening is debated. For healthy adults without risk factors, it is not necessarily cost-effective. However, for the elderly, people with dark skin, the obese, people with malabsorption, or those taking medications that affect vitamin D metabolism, a measurement may make sense. PMID 23853635 PMID 22356356

Myths about vitamin D and aging

Vitamin D is sometimes marketed as a universal anti-aging pill, but the evidence doesn't support that narrative. Large randomized trials such as the VITAL trial did not find that vitamin D supplementation reduced the risk of cardiovascular disease or cancer in non-deficient individuals. Smaller studies have suggested effects on telomere length and epigenetic age, but results are inconsistent and often small. PMID 22356356 PMID 37156805

This does not mean that vitamin D is unimportant. This means that its role in aging is probably as a necessary but not sufficient factor. Like oxygen and water, they are essential for survival without being miracle cures for aging. PMID 22356356 PMID 37156805

Practical recommendations

For most Danish adults, a daily dose of 10-20 micrograms (400-800 IU) in winter is a reasonable starting point. If a deficiency is detected, higher doses are often recommended for a period, followed by maintenance. Fatty meals improve absorption, as vitamin D is fat-soluble. PMID 37156805

Summer sunshine is still the most effective source of vitamin D. About 15-30 minutes of sun on the arms and face in the middle of the day, a few times a week, is often enough for fair-skinned people in the summer months. But sunscreen, clothing and time indoors reduce production significantly. PMID 37156805