Vitamin D is a popular supplement because deficiency is so common. If you are taking a D supplement that gives you 100% of your Recommended Daily Value, the excess gets stored in your body fat and it’s released over time into your blood stream.
Being on a large dose of Vitamin D for a long period of time can cause toxicity. Symptoms of D toxicity can include but aren’t limited to mild/moderate headache, fatigue, nausea, cramps, constipation, confusion, dizziness and slurred speech.
These milder symptoms are all caused in some way by a build up of calcium in the blood. As this core problem gets worse, the symptoms become worse as well, leading up to kidney failure and bone loss.
The full article from Healthline is here and filled with lots of practical patient examples. Totally worth a read.
Personally, I love Vitamin D and have experienced a huge boost in energy since I started taking it. I recommend it highly to people but always with the advice to take it intuitively.
By this I mean you have so many natural sources of D at your disposal, so if your diet (3 oz fatty fish) or your sun exposure (5 – 30 minutes a day) are adequate for the day, you shouldn’t need to add any additional supplementation that day and you can probably even skip it the next.
If you are able to check your micronutrient levels periodically, it will save you a lot of hassle and probably money in the long run. It can help you avoid spending for supplements you don’t need and it will point out gaps that you can fill to optimize your health.