Quick version
Despite the summer sun, not everyone gets enough vitamin D. The skin's own production is severely limited by factors such as indoor work, full-coverage clothing, darker skin tone and advanced age, which means that certain risk groups need supplements all year round. At the same time, more is not always better; overdosing via supplements can be directly harmful to the body, and common summer fatigue is rarely due to vitamin deficiency. For healthy individuals without specific medical conditions or risk factors, there is therefore no reason to either take high doses on their own or have routine blood tests.
When the light returns, many people think that the question of vitamin D is solved for the rest of the year. People are outside more, their skin is exposed more, and supplements often go far back into the bathroom cupboard. But summer does not automatically bring all vitamin D levels back to normal — and for some people, the sun is surprisingly insufficient.
Myth 1: “In the summer, everyone gets enough vitamin D”
That's not true. In Sweden, the skin can form D-vitamin from the sun mainly during the summer months, but that does not mean that everyone actually builds up sufficient levels. How much is formed is affected by how often you are outside, how much skin surface is exposed, skin pigmentation, age, and whether you avoid the sun in the middle of the day.
A person who works indoors all summer, commutes early and late, and mostly spends time outside in the shade may therefore get significantly less vitamin D than you think. The same applies to someone who wears full-coverage clothing or spends very little time outdoors. For these groups, summer can be bright, but still low in vitamin D.
Older people also produce less vitamin D in their skin than younger people. Even people with dark skin usually need longer sun exposure to produce the same amount of vitamin D as a person with light skin. Therefore, “summer” is not a medical answer — it is only a possible source.
Myth 2: “If I am tired in the summer, it is probably due to a vitamin D deficiency”
Fatigue can occur with Vitamin D deficiency, but the symptom is nonspecific. This means that the same problem can also be due to lack of sleep, stress, iron deficiency, thyroid disease, infection, depression or recovery from an intense spring. Guessing based on fatigue alone is therefore often wrong.
With a more pronounced deficiency, adults can develop muscle weakness, diffuse pain in the bones and muscles and, in the long term, osteomalacia, i.e. the bones become insufficiently mineralized. In children, severe deficiency can lead to rickets. Such conditions are something completely different from normal summer fatigue after vacation planning, heat or poor sleep.
It is common for those who feel "sluggish" in July to start taking high doses on their own. Medically, however, it is better to think more broadly: is there also pallor, shortness of breath, palpitation, snoring, weight loss, stomach problems or long-term pain? In that case, the cause should be investigated instead of locking yourself to a single vitamin.
Facts: Vitamin D in the summer is about both sun, skin and lifestyle
Vitamin D is formed in the skin through UVB radiation. In Sweden, it is precisely the stronger sun in the summer that makes this possible, while the winter light is not enough. At the same time, there is a clear seasonal variation, the levels are usually higher at the end of summer and lower during winter and spring.
This means that two people can live in the same city but have completely different conditions. One person cycles to work, eats fish and spends time outside every day. The other works at night, sleeps off the sunniest hours, wears full-coverage clothing and rarely eats vitamin D-fortified foods. Their vitamin D levels can differ significantly despite the same calendar date.
Diet also plays a role, especially in Sweden where many months have little or no skin production. Fatty fish, eggs and vitamin D-fortified foods can contribute, but for many people, diet alone is not enough all year round. Therefore, good vitamin D status is often based on a combination of summer exposure, diet and, if necessary, supplementation.
Myth 3: “The more vitamin D I take, the better I feel”
There is no support for the idea that healthy adults generally become healthier by taking more than recommended just to be on the safe side. Healthy adults under 75 generally do not benefit from taking doses higher than the recommended daily intake, and routine testing is also discouraged in otherwise healthy people who do not have specific risk factors.
This is an important clarification that effectively busts one of our most persistent myths. Vitamin D is necessary for calcium absorption and bones, but more is not automatically better for the immune system, mood, heart or general performance. For many of the broad health effects often mentioned in advertising and social media, the evidence is either uncertain or insufficient in healthy populations.
Excessive doses via supplements can also be harmful. Excess vitamin D is almost always due to excessive intake of dietary supplements, not sun exposure. When levels become too high, calcium in the blood can rise, which can cause nausea, thirst, frequent urination, muscle weakness and, in severe cases, kidney damage or heart rhythm disorders.
For adults, there is an upper tolerable limit of 100 micrograms per day, which corresponds to 4,000 IU, from food and supplements combined. This limit is not a goal to aim for, but a level that should not normally be exceeded without medical prescription and monitoring.
Facts: Some need to think about vitamin D all year round — even during the summer
Not everyone needs to take supplements in the summer, but some groups are at increased risk of low levels year-round. These include people who rarely spend time in the sun, wear clothing that covers most of their skin, have dark skin, are older or have diseases that affect absorption in the intestines. Certain dietary patterns with low intake of fish and fortified products may also contribute.
Swedish advice states that anyone who wears full-covering clothing outdoors even in summer or is not out in the sun during the summer is recommended to take a supplement of 10 micrograms of vitamin D per day. Risk groups may need a daily supplement all year round, while others are mainly recommended to consider supplements during autumn and winter.
Pregnant women, small children and the elderly may also need special assessment. For children, there is special Swedish advice on vitamin D supplements, and those responsible for the elderly at home or in care should be aware that old age itself reduces the skin's ability to form vitamin D.
When should you test vitamin D?
If you are otherwise healthy, have no symptoms and do not belong to a risk group, there is no strong support for testing vitamin D routinely. Sampling becomes more relevant when there is a specific medical issue. Examples include long-term muscle weakness, bone pain, repeated low-energy fractures, suspected malabsorption, previous gastric bypass, inflammatory bowel disease, chronic liver disease, kidney disease or medications that affect vitamin D metabolism. In this case, the 25-hydroxyvitamin D blood test is the test normally used to assess the body's vitamin D status.
It may also be reasonable to test if you are already taking high-dose supplements and want to know that the level is correct. A blood test then provides better guidance than continuing on a gut feeling. Often, it is precisely the combination of symptoms, risk factors and test results that makes the assessment medically accurate.
Summer is therefore not a confirmation that the vitamin D issue is resolved. For those who work a lot indoors, recover from illness, live with a gastrointestinal disease or rarely get sun on their skin, July can be just as relevant a month for testing as November — especially if you want to make decisions based on facts instead of assumptions.
