Vitamin D Deficiency: Symptoms & Supplementation Advice

Fatigue, infections, hair loss – the symptoms are varied. From October onwards, vitamin D reserves dwindle. This way you can detect the defect early.

While the leaves fall outside and the days become noticeably shorter, a gradual process begins in the body: vitamin D reserves begin to dwindle. “Vitamin D deficiency begins in October,” warns dermatologist Dr. Markus Reinholz. What many people don’t know: According to the German Nutrition Society (DGE), 60 percent of the German population suffers from a suboptimal vitamin D supply. The consequences often appear slowly. But anyone who recognizes the warning signals can take countermeasures in good time.

7 Signs You Don’t Have Enough Vitamin D

In Germany, the body’s own vitamin D synthesis is only possible between March and October, shows a case study by International Journal of Health Sciences and Research (2024). For the rest of the year, the organism draws on its reserves – until they are exhausted. Signs of a deficiency include:

1. Chronic fatigue: The most common and at the same time most underestimated symptom is persistent exhaustion. Vitamin D plays a crucial role in energy production in cells.
2. Increased susceptibility to infection: Vitamin D regulates the production of antimicrobial peptides such as cathelicidin, which are essential for immune defense. A deficiency leads to reduced production of these protective proteins, making it easier for viruses and bacteria to pass through.
3. Dejection to depression: Vitamin D activates a key enzyme for serotonin production in the brain. An observational study (2013) suggests that vitamin D deficiency is linked to depression and seasonal affective disorder. However, further controlled studies are needed to clearly demonstrate the exact role of vitamin D in mental illness.
4. Bone and back pain: Vitamin D is essential for calcium absorption in the intestines. According to a study (2025), if there is a deficiency, the body can only use 10 to 15 percent of the available calcium, instead of the normal 30 to 40 percent.
5. Muscle weakness and pain: Muscle weakness is one of the classic symptoms of vitamin D deficiency. Those affected report a feeling of “heavy legs”, difficulty climbing stairs or frequent falls. Neuromuscular coordination suffers, which increases the risk of falls, especially in older people.
6. Hair loss: Vitamin D regulates the hair follicle cycle. A study (2014) shows a clear connection between low vitamin D levels and hair loss. Women are particularly affected, and hair loss often only becomes visible months after the deficiency begins.
7. Poor wound healing: A study (2023) shows that vitamin D plays a central role in inflammatory processes and cell regeneration. Small injuries that would normally heal within days suddenly take weeks. Gum problems or surgical wounds that heal poorly can also be indications of a deficiency.

Also exciting: myths about vitamin D and what is really behind it.

Vitamin D deficiency: who is particularly at risk – and why

People over 65 years of age are particularly at risk, as vitamin D synthesis in the skin decreases with age, office workers with little daylight, people with dark skin in northern European latitudes and overweight people, as vitamin D is “locked” in fatty tissue, according to a report by the Robert Koch Institute (RKI). Dr. In this context, Reinholz emphasizes that almost everyone in the northern European population has a deficiency.

Test vitamin D status

A blood test to determine the vitamin D level provides clarity. The DGE defines vitamin D deficiency as serum concentrations below 30 nmol/L (12 ng/ml). A good vitamin D supply for bone health is at least 50 nmol/L (20 ng/ml).

But when does a test make sense? The DGE recommends a determination only “if there is reasonable suspicion of a deficiency situation or for people at risk”. If there is a deficiency, it makes sense to take 20 micrograms daily.

This is how you prevent a vitamin D deficiency

In the summer months, just 15 to 20 minutes of sun exposure on the face and arms two to three times a week is enough to cover your vitamin D needs. However, this calculation only works from March to October. Certain foods can also have a supportive effect – you can find a complete overview in our free vitamin D food list. However, food alone is not enough to meet winter needs. “That’s why you should definitely supplement vitamin D, at least from October to April or even May,” advises Dr. Purewood.

Winter wellness: Our series of articles for your health

Vitamin D is just the beginning: In our “Feel-Good Winter” series you will find out how you can increase your well-being in the dark season. Next up: winter blues or depression – what’s the difference? This is followed by practical light impulses for November and an overview of important nutrients in winter. Be excited about your health in the cold season.