Constant fatigue, sleepiness, and feeling like you have “no energy” even in April — familiar situation? Often this is attributed to spring, but one of the causes may be vitamin D deficiency. After a long winter, its levels drop, there are still not enough sunny days, and the symptoms can easily be confused with ordinary “spring fatigue.” Let’s look at why this happens, which signals should not be ignored, and what to do without taking high doses on your own.
Spring is expected to bring more energy, but in practice many experience the opposite: less strength, increased sleepiness, reduced concentration, and more frequent colds. After cold months, vitamin D levels often fall, especially if there was little sun in winter, you rarely went outside, or your diet contained almost no sources of this vitamin.
Why Vitamin D Deficiency Appears in Spring
Reduced Sunlight After Winter
The simplest explanation is this: by April, we often approach with an “empty tank.” NHS notes that between October and early March, in many latitudes there is not enough sun for the skin to produce the required amount of vitamin D, meaning that by the end of winter and the beginning of spring, the risk of deficiency is logically higher. Even if by late March or April there is more sun, the level won’t instantly rise after just a few walks.
There are other factors that exacerbate the problem. Dark skin type, older age, excess weight, sedentary lifestyle, covering clothing, office work, night shifts, rare daytime walks — all these reduce the chances of adequately synthesizing vitamin D even when spring has officially begun. A separate story is people with intestinal, liver, or kidney diseases, or those taking certain medications — their risk is also higher.
Impact on Immunity and Mood
Vitamin D is needed not only for bones. According to NIH, it participates in the functioning of the immune system, muscles, and nervous system, and also affects calcium and phosphorus metabolism. This does not mean that every bad mood or cold is automatically caused by it, but with its deficiency, a person can indeed feel worse.
Mood is not as simple as social media often suggests. Spring lethargy can be linked to sleep, stress, seasonal changes, anxiety, iron or B12 deficiency, and overwork. But low vitamin D levels can also be one piece of the puzzle, especially if strength, endurance, and overall well-being decrease along with mood. So it should not be blamed for everything, but it should not be ignored either.
Table 1. Why Vitamin D Becomes Relevant Specifically in April
| Factor | What Happens | Why It Matters |
|---|---|---|
| Long Winter | Few months with insufficient UVB for vitamin D synthesis | By spring, reserves may be low |
| Indoor Work | Person rarely exposed to daylight | Spring sun is present, but skin “does not see it” |
| Few Dietary Sources | Vitamin D naturally low in foods | Hard to cover needs through diet alone |
| Dark Skin Type | Longer sun exposure needed for vitamin D synthesis | Higher risk of deficiency |
| Older Age | Skin synthesizes vitamin D less efficiently | Levels may recover more slowly even in spring |
Symptoms That May Signal Deficiency
Here, it is important to avoid drama. Vitamin D deficiency rarely comes with a sign saying “this is me.” Its manifestations are often nonspecific, resembling dozens of other conditions. That is why people for months attribute everything to weather, work, children, deadlines, magnetic storms, or anything else.
Fatigue and Sleepiness
One of the most common scenarios: a person wakes up already exhausted. Not collapsing, but with less energy, worse concentration, and by evening just “shuts down.” This is not a unique sign of vitamin D deficiency, but it often accompanies it. In pronounced deficiency, muscle weakness, aches, or discomfort in bones or joints may appear.
If cramps, muscle pain, difficulty climbing stairs, or a feeling of a “heavy body” accompany fatigue, this is a strong reason to consult a doctor rather than guessing. Because the issue may involve not only vitamin D but also calcium, thyroid, anemia, or other causes.
Increased Susceptibility to Colds
Vitamin D is linked to normal immune function, and clinical nutrient deficiency in general can increase vulnerability to infections. But let’s be honest: it is not a magic “never get sick” button. Frequent colds can result from a combination of factors, from stress and lack of sleep to contact with children, chronic illnesses, or just a busy schedule without recovery.
The logic is simple: repeated colds alongside fatigue, muscle pain, low mood, and minimal sun exposure in recent months are already a reason to check the situation, rather than just buying another “immune booster” from advertising.
Safe Ways to Maintain Vitamin D Levels
The main rule is very down-to-earth: do not self-treat with high doses because “my friend took 10,000 IU and it worked for her.” Excess vitamin D is also harmful. NIH and NHS warn that toxicity is mainly linked to excessive supplement intake, and for adults the upper safe daily intake is 100 µg, i.e., 4000 IU, unless prescribed otherwise by a doctor.
Dietary Sources
With food, it’s straightforward: getting enough vitamin D from diet alone is difficult, but nutrition still matters. The best-known sources are fatty fish, egg yolks, liver, and some fortified foods, like cereals, milk, or plant-based drinks if the manufacturer adds vitamin D. Food rarely corrects a severe deficiency, but works well as part of a normal support strategy.
Another overlooked point: vitamin D is fat-soluble, so it is better absorbed with some dietary fat. This is not an excuse to pour mayonnaise on everything, but taking a supplement on an empty stomach and expecting results is also not the smartest plan.
Doctor Supervision When Needed
Current recommendations are more cautious than a few years ago. The Endocrine Society 2024 guideline does not recommend routinely testing 25(OH)D for everyone without indications. But if there are symptoms, risk factors, diseases affecting absorption or metabolism, or suspected severe deficiency, a doctor can order tests and prescribe a tailored dosage. This is a proper approach, not guessing based on TikTok.
For some people, preventive supplementation may indeed be appropriate, but the dose should be adjusted for age, health status, diet, sun exposure, and associated risks. NIH provides approximate daily requirements: 600 IU for most people aged 19–70 and 800 IU for those 71+. This is not a universal “internet recipe,” but a basic orientation.
Table 2. What Can Be Done Safely Now
| Action | Who It Suits | What to Remember |
|---|---|---|
| Add fatty fish, eggs, and fortified foods to your menu | Almost everyone | Food is important but does not always fully cover deficiency |
| Spend time outdoors during the day regularly | Those mostly indoors | Spring sun helps, but the effect is not instant |
| Discuss supplements with a doctor or family physician | People with symptoms or risk factors | Especially important for chronic illnesses, pregnancy, older age |
| Do not exceed 4000 IU* per day without necessity | Anyone taking supplements themselves | High doses without supervision can be harmful |
| Do not test “just in case” without reason | People without symptoms or risks | Routine testing for everyone is not recommended |
*4000 IU — upper tolerable intake level (UL), not a standard recommendation.
When Not to Delay
If there is persistent pronounced weakness,
When Not to Delay
If there is persistent pronounced weakness, bone pain, frequent falls, muscle weakness, cramps, numbness, or a person belongs to a risk group and is feeling genuinely unwell, it’s better not to play at home endocrinology. The same applies to pregnant women, elderly people, adolescents during periods of rapid growth, people with intestinal, kidney, or liver diseases, osteoporosis, or those taking certain medications for a long time.
Questions & Answers
Can vitamin D deficiency worsen in April?
Yes. Vitamin D deficiency typically develops during winter, when sunlight is insufficient. In April, it does not appear “from scratch,” but becomes more noticeable due to the accumulated deficiency after the cold months.
Is it enough to spend more time outdoors in spring to boost vitamin D?
Not always. Sunlight helps, but if vitamin D levels are already low, walks alone may not be sufficient. In some cases, additional correction under a doctor’s supervision is necessary.
What are the most common symptoms of vitamin D deficiency?
Most often it is fatigue, drowsiness, muscle weakness, decreased endurance, and frequent colds. Sometimes muscle or bone pain may appear. It is important to note that these symptoms are not specific and require a comprehensive assessment.
Can I take high doses of vitamin D on my own?
No, it is dangerous. Prolonged intake of high doses without supervision can lead to side effects. For most adults, exceeding 4000 IU per day without a doctor’s prescription is not recommended.
Should everyone get a vitamin D test in spring?
No. Routine testing without symptoms or risk factors is not recommended. However, if symptoms are present or deficiency is suspected, a doctor may order a 25(OH)D test.
Conclusions
If persistent fatigue, drowsiness, and a feeling of low energy appear in spring, it may be related to vitamin D deficiency after winter. In April, these symptoms become especially noticeable, even with increasing sunlight. In such situations, it is important not to ignore the body’s signals, but also not to draw hasty conclusions.
The optimal strategy is moderation: more daylight, balanced nutrition, and cautious use of supplements. If symptoms or risk factors are present, it is worth consulting a doctor to assess vitamin D levels and select the appropriate dosage. This approach is more effective and safer than self-administering high doses.
References
- Office of Dietary Supplements, NIH. Vitamin D: Fact Sheet for Health Professionals. Updated June 27, 2025.
- Office of Dietary Supplements, NIH. Vitamin D: Fact Sheet for Consumers.
- NHS. Vitamin D. Data on seasonal synthesis, sources, and safe upper intake limits.
- Endocrine Society. Vitamin D for the Prevention of Disease Guideline Resources, June 3, 2024.
- Demay MB, et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. 2024;109(8):1907-1947. doi:10.1210/clinem/dgae290.
- NICE. Vitamin D: supplement use in specific population groups. Review of risk groups. Last updated December 9, 2025.
- NHS. Rickets and osteomalacia. Signs of bone pain and muscle weakness.
- ODS, NIH. Dietary Supplements for Immune Function and Infectious Diseases. Updated March 10, 2025.
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