Understanding the Effects of Vitamin D Toxicity
I’m a big believer in the role of vitamin D in optimizing your health. As noted in previous articles, it’s been shown to help promote a diverse range of functions, including mental health, skeletal health, and immune function.
However, there’s one topic about vitamin D that deserves more attention — toxicity. Just as a deficiency will lead to various health problems, it’s important to maintain a proper balance because too much vitamin D will also cause problems. This issue, as well as other topics, was explored by Reinhold Vieth, Ph.D., during a presentation at the University of Minnesota, which I will summarize below.
Vitamin D Metabolism Explained
Vieth begins his presentation, featured in the video above, by providing an overview of how vitamin D is produced and metabolized in your body.
• Your skin creates an early version of vitamin D — This precursor substance travels through your bloodstream to your liver, where it is converted into 25-hydroxyvitamin D. When your doctor asks for a vitamin D blood test, this is the vitamin D measurement they’re looking for.1
• The kidneys help synthesize vitamin D — To become fully active, 25-hydroxyvitamin D then travels to your kidneys, where it is converted into 1,25-dihydroxyvitamin D, which works more like a hormone.
This active form helps your intestines absorb calcium from the food you eat. It also supports a stable environment in your body by making sure cells get what they need to function correctly. Your body stores this nutrient in places such as your muscles and fatty tissue.2
• An easy way to understand how vitamin D is created — To paint a picture explaining this process, visualize the flow of vitamin D as if it moves through several buckets, each one connected by holes that let the vitamin drop to the next step. The first bucket is the form made in your skin. The second is the 25-hydroxyvitamin D in your liver. The third is the active 1,25-dihydroxyvitamin D produced in your kidneys.
The reason proper vitamin D levels matter is that this nutrient does not act alone. It works alongside calcium and other substances to keep many parts of your body healthy. Two common symptoms of vitamin D deficiency include fatigue and brittle bones. However, too much vitamin D also has its risks.
Balancing Calcium with Vitamin D — Your Body’s Tightrope Act
Another crucial topic that Vieth discusses is the interaction between vitamin D and calcium. Essentially, vitamin D boosts your ability to absorb calcium from meals.
• Vitamin D increases the bioavailability of calcium — When you eat foods rich in calcium, such as dairy products, your intestines take in more of that mineral if there is enough vitamin D available. In addition to supporting your bones, calcium is important for muscle and nerve health.
• Parathyroid hormone (PTH) also supports calcium management — It acts as a messenger in your body’s calcium system. When calcium levels are low, PTH sends signals to your bones to release some calcium into your bloodstream. Vitamin D works alongside PTH by helping your body absorb calcium from food through your digestive system, which helps replenish your bones.3
If your vitamin D level is too high, your blood calcium levels become excessive, leading to hypercalcemia. You’ll feel thirstier, develop fatigue faster, or sense that your digestive habits have changed. Although hypercalcemia is rare, it does occur if you take large doses of supplemental vitamin D on a regular basis.4
Effects of Vitamin D Overload
While low levels of vitamin D are not good, mega-doses put extra stress on your system. If you already get enough vitamin D from sun exposure and/or moderate supplementation, swallowing more won’t make you healthier.
• Symptoms of excess vitamin D — In Vieth’s presentation, he tells the story of a 29-year-old man who was experiencing a wide range of symptoms, such as vomiting, increased thirst, and acute renal failure. At first, doctors diagnosed him with gastroenteritis, saying he’ll eventually feel better.
However, the man had to return, and now, doctors took him seriously. They tested his blood, which contained 3.72 mmol/L of calcium (normal is 2.20 to 2.65 mmol/L), as well as a whopping 1,555 nmol/L of vitamin D (normal is 20 to 80 nmol/L).5
• Fortified products drastically increase your vitamin D levels — Eventually, the man’s father had to be admitted to the same hospital for similar symptoms. After investigating their eating habits, Vieth noted that the father and son’s table sugar was fortified with pure vitamin D, about a milligram per teaspoon. Eventually, they made a full recovery when the fortified table sugar was removed.6
Setting the Foundation to Optimized Vitamin D Levels
The takeaway is that excessive vitamin D intake from food or supplements are just as harmful as having too little. So, it’s important to be mindful of supplement dosages and not exceed recommended amounts.
• Exposing your skin to natural sunlight at appropriate times is the best approach — However, there are certain caveats you need to be aware of, such as your diet, which is most likely high in linoleic acid (LA). When ultraviolet light hits your skin, it also interacts with LA that triggers inflammatory responses and DNA damage. As a result, high-LA diets make you more prone to sunburn and skin damage.
• Take a more careful approach to sun exposure as you work to purge LA from your body — I recommend avoiding high-intensity midday sun exposure until you’ve been off vegetable oils for at least six months.
As you gradually eliminate LA from your body — a process that typically takes two to three years — your risk of sunburn and skin cancer declines. However, after about six months, your skin is usually better protected against sunburn, allowing you to safely enjoy sun exposure around solar noon.
• Consider your skin color when optimizing your vitamin D — Melanin, responsible for skin pigmentation, also acts as a natural sunscreen. This means that if you have darker skin, you’ll need more time under the sun to generate the same amount of vitamin D as those with lighter complexions.
Additional Guidelines for Safe Sun Exposure
When you begin getting regular sun exposure, use this simple safety test: watch your skin for the first sign of pinkness, which is an early warning of sunburn. Stop sun exposure before your skin turns pink to prevent damage. This pinkness threshold helps you determine your safe exposure time.
Now, what if you need to spend time under the sun but haven’t completely removed LA from your body yet? Here are some protective strategies I recommend:
• Take 12 milligrams of astaxanthin daily to enhance your skin’s UV resistance.
• Apply topical niacinamide (vitamin B3) cream before sun exposure to protect against UV-induced DNA damage.
• Take a baby aspirin 30 to 60 minutes before sun exposure to help prevent LA conversion to harmful oxidized linoleic acid metabolites (OXLAMs).
• Use molecular hydrogen supplements to combat oxidative stress.
How to Supplement Vitamin D Properly
While most people would probably benefit from a vitamin D3 supplement, it’s important to get your vitamin D level tested before you start supplementing.
• You cannot rely on blanket dosing recommendations — The crucial factor here is your blood level, not the dose, as the dose you need is dependent on several individual factors, including your baseline blood level.
• The sweet spot for harnessing the benefits of vitamin D — Research suggests the optimal level for health and disease prevention is between 60 ng/mL and 80 ng/mL, while the cutoff for sufficiency appears to be around 40 ng/mL. In Europe, the measurements you’re looking for are 150 to 200 nmol/L and 100 nmol/L respectively.
I’ve published a comprehensive vitamin D report in which I detail vitamin D’s mechanisms of action and how to ensure optimal levels. I recommend downloading and sharing that report with everyone you know. A quick summary of the key steps is as follows:
1. First, measure your vitamin D level — Once you know what your blood level is, you can assess the dose needed to maintain or improve your level. If you cannot get enough vitamin D from the sun (you can use the DMinder app7 to see how much vitamin D your body can make depending on your location and other individual factors), then you’ll need an oral supplement.
2. Assess your individualized vitamin D dosage — To do that, you can either use the chart below, or use GrassrootsHealth’s Vitamin D*calculator. To convert ng/mL into the European measurement (nmol/L), simply multiply the ng/mL measurement by 2.5. To calculate how much vitamin D you may be getting from regular sun exposure in addition to your supplemental intake, use the DMinder app.8
3. Retest in three to six months — Lastly, you’ll need to remeasure your vitamin D level in three to six months, to evaluate how your sun exposure and/or supplement dose is working for you.
Take Your Vitamin D With Magnesium and K2
It’s strongly recommended to take magnesium and K2 concomitant with oral vitamin D. Data from nearly 3,000 individuals reveal you need 244% more oral vitamin D if you’re not also taking magnesium and vitamin K2.9
What this means in practical terms is that if you take all three supplements in combination, you need far less oral vitamin D in order to achieve a healthy vitamin D level.
Frequently Asked Questions (FAQs) About Vitamin D Toxicity
Q: Why is vitamin D important for health, and how is it processed in my body?
A: Vitamin D supports your mental, skeletal, and immune health. It is produced in the skin from sun exposure, then converted in the liver to 25-hydroxyvitamin D, and finally activated in the kidneys as 1,25-dihydroxyvitamin D. This final form helps absorb calcium and maintain cell function.
Q: Can I have too much vitamin D? If so, what are the risks?
A: Yes, excessive vitamin D leads to hypercalcemia (high blood calcium), causing symptoms like fatigue, thirst, digestive issues, and even kidney failure. This occurs with chronic supplementation or consuming fortified foods unknowingly.
Q: How does vitamin D interact with calcium and other nutrients?
A: Vitamin D enhances calcium absorption from food, which is essential for bone, muscle, and nerve health. It works with parathyroid hormone (PTH) to maintain calcium balance. Supplementing with magnesium and vitamin K2 is also crucial, as they help vitamin D function efficiently and safely.
Q: What’s the safest way for me to get vitamin D from sunlight?
A: Expose your skin to sun just before it turns pink to avoid sunburn. If your diet is high in linoleic acid (from vegetable oils), it increases sun sensitivity. Reducing LA intake over time and using protective strategies (like astaxanthin or niacinamide) help your skin handle UV exposure better.
Q: How should I supplement vitamin D correctly?
A: Start by testing your blood levels. The optimal range is 60 to 80 ng/mL (150 to 200 nmol/L). Use tools like the DMinder app or GrassrootsHealth’s calculator to assess sun exposure and determine the right supplement dose. Retest every three to six months to adjust intake as needed.
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