Vitamin D3 supplements help improve bone strength, muscle function, and recovery, especially if your levels are low or you spend less time in sunlight. A doctor may advise a suitable dose based on your level, as some people need a weekly high dose for deficiency, while others can take a low daily dose for maintenance. It is usually safe when taken correctly, but high doses can cause side effects like nausea or weakness if taken without advice. It is best to check your vitamin D level and consult your doctor to choose the right option and dose.