If your vitamin D levels are too high over a significant time period this may cause too much calcium to build up in the body which can result in weakened bones, and damage to the kidneys and the heart. Therefore, it is important to regularly get your vitamin D levels tested when taking high strength Vitamin D3 drops or tablets. Vitamin D levels are considered to be too high and in the range for toxicity when they are >374nmol/litre (>150ng/ml).