Vitamin D has long been promoted as an essential nutrient, especially during the darker winter months when limited sunlight can increase the risk of deficiency. But medical experts are now cautioning that vitamin D supplements aren’t always harmless — and in certain situations, they may do more harm than good.
Doctors say that if people experience specific symptoms after taking vitamin D, they should pause supplementation and consult a healthcare professional.
Why Vitamin D Matters
According to the Cleveland Clinic, vitamin D — also known as calcitriol — is a fat-soluble vitamin with two primary functions: helping the body absorb calcium to maintain strong bones and supporting immune system function.
Health experts estimate that roughly 35% of adults may be deficient in vitamin D, with some studies suggesting the number could be even higher.
“Our bodies naturally produce vitamin D through sun exposure,” explained registered dietitian Devon Peart. “It’s also found in certain foods like salmon and fortified products such as milk. Depending on where you live and how much sun you get, supplements may be necessary.”
Vitamin D plays a critical role in bone density, calcium absorption, and immune defense — making it one of the most commonly purchased dietary supplements worldwide.
Recommended Intake — and When It Becomes Too Much
The Cleveland Clinic outlines general daily intake guidelines:
- 600 IU for adults ages 19–50
- At least 600 IU for adults ages 50–70
- At least 800 IU for adults over 70
However, because vitamin D is fat-soluble, excess amounts can accumulate in the body. Medical professionals warn that over-supplementation may lead to vitamin D toxicity, a condition linked to serious health risks, including kidney complications.
Symptoms That May Signal Vitamin D Toxicity
Doctors advise stopping vitamin D supplements and seeking medical advice if any of the following symptoms appear:
- Frequent urination
- Nausea or vomiting
- Dehydration
- Constipation
- Bone pain
- Kidney stones
These symptoms may indicate elevated calcium levels in the blood, which can strain the kidneys and affect overall health.
What Medical Experts Are Saying
Speaking to The Independent, Dr. Kathryn Basford of Asda Online Doctor explained that while vitamin D is beneficial during winter months — particularly in the UK — moderation is essential.
“Most people can benefit from vitamin D in darker months,” she said. “It’s difficult to get enough from diet alone, and deficiency can lead to fatigue, muscle pain, bone discomfort, and frequent infections.”
However, she also warned that excess intake of fat-soluble vitamins — including vitamins A, D, E, and K — can lead to toxicity because the body stores them rather than flushing them out.
“This only occurs with supplements,” she noted. “Vitamin D from food or sunlight doesn’t pose the same risk.”
When Supplements Backfire
Biomedical scientist Tobias Mapulanga explained that many people increase their supplement intake in winter — sometimes combining pills, sprays, and gummies — without realizing they may be exceeding safe limits.
Symptoms such as constant thirst, increased urination, nausea, abdominal discomfort, constipation, headaches, brain fog, or new muscle aches appearing shortly after increasing vitamin D intake may indicate that supplementation is having the opposite effect.
A Reminder for Smart Supplement Use
Vitamin D remains an important part of preventive healthcare and bone health, but experts stress the importance of following recommended doses and consulting a medical professional before increasing intake — especially for those with kidney disease or other underlying conditions.
If you take vitamin D supplements, this is a helpful reminder that more isn’t always better when it comes to health and wellness.
Always consult a healthcare provider before stopping or changing any supplement regimen.