Vitamin D is a fat-soluble vitamin that you need for calcium balance and bone health, proper immune system function, blood pressure regulation and blood sugar control. Healthy adults can make their own vitamin D if they get adequate sunlight, but if you are older, have dark skin, or get very little sunlight you may need additional vitamin D. Only take a supplement if your doctor recommends one, and if you are taking a vitamin D supplement with 50,000 IU of vitamin D and you are having back pain, contact your doctor as soon as possible.
The daily value for vitamin D is 400 IU, and the Linus Pauling Institute Micronutrient Information Center states that this dose is based on the amount that is probably sufficient for a healthy adult on a 2,000-calorie diet to support normal bone development and maintenance with an overall healthy diet. A dose of 50,000 IU of vitamin D each day is more than 100 times the daily value, but your average intake is less if you are taking that dose as a less frequent supplement, such as monthly.
According to the Linus Pauling Institute Micronutrient Information Center, certain individuals may get extra health benefits, such as a lower risk for osteoporosis or high blood pressure, from taking a supplement that provides up to about 4,000 IU, which is more than the recommended daily value. The tolerable upper intake level, or UL, is the amount that is considered safe for long-term daily intake, and for vitamin D, the UL is 4,000 IU. If you are taking 50,000 IU daily, you are taking more than 10 times the UL for safety. This may put you at risk for side effects.
Vitamin D Overdose
You cannot get vitamin D toxicity from exposure to sunlight, but the National Institutes of Health state that too much vitamin D from supplements can lead to high levels of vitamin D in your blood, and health problems such as weight loss, pancreatic cancer or an irregular heartbeat. If you take more than 50,000 IU vitamin D each day, you may get hypercalcemia, or high levels of calcium in your blood, and the Mayo Clinic states that symptoms may include muscle and joint aches.
High doses of vitamin D could lead to hypercalcemia and pain in your back muscles, but back pain can result from a variety of other causes. You could have an undiagnosed vertebral fracture, or you could have a pulled back muscle or a pinched nerve from straining your back or exercising. To be safe, you should call your doctor if you have pain in your back, and avoid activities that increase the pain.