Vitamin D plays an important role in maintaining our good health. It’s necessary for the growth and development of our muscle cells, proper functioning of the immune system, maintenance of the health of our skeletal system, and more.
Vitamin D deficiency is common, and many people take vitamin D supplements to replenish their levels. From those people, Few people may exceed the upper limit of Vitamin D dose per day which may cause Vitamin D toxicity.
Vitamin D toxicity is rare, but it may happen with extremely too much vitamin D.
It usually develops over time, because too much vitamin D can accumulate in our bodies.
Mostly all vitamin D overdoses come from taking too much vitamin D supplements, and it isn't possible to get too much vitamin D from sunlight or food.
This is a detailed article about vitamin D overdoses and how much of it is considered to be too much vitamin D.
How does vitamin D toxicity happen?
Hypervitaminosis D is defined as blood vitamin D levels over 100 ng/mL, while vitamin D intoxication is defined as serum levels over 150 ng/mL
Vitamin D is a fat-soluble vitamin and our bodies can't remove excess fat soluble vitamins like vitamin D easily in contrast to water-soluble vitamins.
For this reason, excess amounts may accumulate inside our body, but the mechanism of this isn't fully understood till now.
However, we know that vitamin D active form works in a similar way as a steroid hormone.
It travels inside cells, telling them to turn genes on or off.
Usually, most of the body’s vitamin D is stored, bound to either vitamin D receptors or carrier proteins, and very little “free” vitamin D is available.
However, when vitamin D intake is too much, the levels become so high that there isn’t any room left on the receptors or carrier proteins.
This may increase “free” vitamin D levels in the body, which may travel inside cells and overwhelm the signaling processes affected by vitamin D.
One of the main signaling processes has to do with increasing calcium absorption from the digestive system.
So, the main symptom of vitamin D toxicity is hypercalcemia (high levels of calcium in the blood).
High calcium levels can cause various symptoms, and the calcium can also bind to other tissues and damage them including the kidneys.
Vitamin D blood levels: Optimal vs. too much vitamin D
Vitamin D is an essential vitamin, and almost every cell in our body has a receptor for it. It’s produced when the skin is exposed to sun.
The main dietary sources of vitamin D are fish liver oils and fatty fish.
For people who don’t get enough sunlight, vitamin D supplements are important.
Guidelines for blood levels of vitamin D are as follows:
- Sufficient: 20–30 ng/mL, or 50–75 nmol/L
- Safe upper limit: 60 ng/mL, or 150 nmol/L
- Toxic: above 150 ng/mL, or 375 nmol/L
A daily vitamin D intake of 1,000–4,000 IU (25–100 mcg) is enough to ensure sufficient blood levels for most people.
According to the National Academy of Medicine, 4,000 IU is the safe upper level of daily vitamin D intake. However, doses up to 10,000 IU have not been shown to cause toxicity in healthy individuals.
The only trusted way to tell if you’re insufficient or deficient is testing your vitamin D levels.
Healthcare professionals may recommend people who are very low in vitamin D take very high weekly doses of 50,000 IU for 8 weeks, followed by a maintenance dose of 2,000 IU per day after their levels reach 30 ng/mL
Causes of too much vitamin D
- Taking too much vitamin D supplements, not diet or sun exposure is the main cause.
- A daily intake ranging from 40,000–100,000 IU (1,000–2,500 mcg), for 1 to several months
- Several cases have also been caused by errors in manufacturing, when the supplements had 100–4,000 times higher amounts of vitamin D than stated on the package.
Symptoms and treatment of vitamin D toxicity
The main result of vitamin D toxicity is calcium buildup in the blood (hypercalcemia).
Early symptoms of hypercalcemia include:
- digestive distress, such as vomiting, nausea, diarrhea, constipation, and stomach pain.
- loss of appetite and excessive urination
- fatigue, dizziness, hallucinations, confusion and altered level of consciousness
- excessive thirst, an altered level of consciousness, high blood pressure, kidney tubes calcification, kidney failure, or hearing loss.
Hypercalcemia caused by regularly consuming too much vitamin D supplements may take a few months to resolve because vitamin D accumulates in body fat and is released into the blood slowly.
Treating too much vitamin D includes avoiding sun exposure and eliminating all dietary and supplemental vitamin D.
A doctor may also correct your calcium levels with increased salt and fluids, often by intravenous saline.
Too much vitamin D can be harmful, even without toxicity immediate symptoms
Vitamin D is very unlikely to cause severe symptoms of toxicity immediately, and symptoms may take months or years to appear like hypercalcemia and symptoms of kidney failure. This is one reason why vitamin D toxicity is so hard to detect.
The harmful effects of vitamin D are very complex. High doses of vitamin D can cause hypercalcemia without toxicity symptoms, but can also cause toxicity symptoms without hypercalcemia.
To be safe, don't take more than 4,000 IU (100 mcg) without consulting a doctor or dietitian.
Does the intake of other fat-soluble vitamins change vitamin D tolerance?
It has been hypothesized that two other fat-soluble vitamins, vitamin K and vitamin A, may play important roles in vitamin D toxicity.
Vitamin K helps regulate where calcium ends up in the body, and high amounts of vitamin D may deplete the body’s stores of vitamin K.
A higher vitamin A intake may help prevent this from happening by sparing the vitamin K stores.
Another nutrient that may be important is magnesium. It’s one of the elements needed for good bone health.
Taking vitamin A, vitamin K, and magnesium with vitamin D may therefore improve bone function and reduce the chances of other tissues becoming calcified.
Keep in mind that these are just hypotheses, but it may be wise to make sure you’re getting enough of these nutrients if you’re going to supplement with vitamin D.
Briefly
People response varies to high doses of vitamin D. So, it’s hard to evaluate which doses are safe and which are not.
Vitamin D toxicity can have serious health effects, which may take months or even years to appears.
Generally, it’s not recommended to take more than the upper limit of vitamin D safe intake, which is 4,000 IU (100 mcg) per day.
Keep in mind that larger doses have not been linked with any additional health benefits.
An occasional vitamin D high dose is sometimes used to treat a deficiency, but always consult with a doctor or dietitian before taking a large dose.
