A dose of 10 micrograms (400 units) of vitamin D per day has been shown to be safe and effective at preventing vitamin D deficiency. There is no need to take more than this.
Very large doses of over 100 micrograms (4,000 units) per day could be harmful as it could cause high levels of calcium in the body. This may cause problems with the bones, kidneys, and heart.
People with medical conditions which cause high levels of calcium, or kidney problems, might not be able to take as much vitamin D. It is best to discuss the dose of vitamin D with your doctor if you have any questions.
It is not possible to make too much vitamin D from the sunlight. However, it is important to avoid sunburn and skin damage to reduce the risk of skin cancer.