What are some effects of vitamin D on health?
Scientists are studying vitamin D to better understand how it affects health. Here are several examples of what this research has shown:
Bone health and osteoporosis
Long-term shortages of vitamin D and calcium cause your bones to become fragile and break more easily. This condition is called osteoporosis. Millions of older women and men have osteoporosis or are at risk of developing this condition. Muscles are also important for healthy bones because they help maintain balance and prevent falls. A shortage of vitamin D may lead to weak, painful muscles.
Getting recommended amounts of vitamin D and calcium from foods (and supplements, if needed) will help maintain healthy bones and prevent osteoporosis. Taking vitamin D and calcium supplements slightly increases bone strength in older adults, but it’s not clear whether they reduce the risk of falling or breaking a bone.
Vitamin D does not seem to reduce the risk of developing cancer of the breast, colon, rectum, or lung. It is not clear whether vitamin D affects the risk of prostate cancer or chance of surviving this cancer. Very high blood levels of vitamin D may even increase the risk of pancreatic cancer.
Clinical trials suggest that while vitamin D supplements (with or without calcium) may not affect your risk of getting cancer, they might slightly reduce your risk of dying from this disease. More research is needed to better understand the role that vitamin D plays in cancer prevention and cancer-related death.
Vitamin D is important for a healthy heart and blood vessels and for normal blood pressure. Some studies show that vitamin D supplements might help reduce blood cholesterol levels and high blood pressure—two of the main risk factors for heart disease. Other studies show no benefits. If you are overweight or obese, taking vitamin D at doses above 20 mcg (800 IU) per day plus calcium might actually raise your blood pressure. Overall, clinical trials find that vitamin D supplements do not reduce the risk of developing heart disease or dying from it, even if you have low blood levels of the vitamin.
Vitamin D is needed for your brain to function properly. Some studies have found links between low blood levels of vitamin D and an increased risk of depression. However, clinical trials show that taking vitamin D supplements does not prevent or ease symptoms of depression.
People who live near the equator have more sun exposure and higher vitamin D levels. They also rarely develop multiple sclerosis (MS), a disease that affects the nerves that carry messages from the brain to the rest of the body. Many studies find a link between low blood vitamin D levels and the risk of developing MS. However, scientists have not actually studied whether vitamin D supplements can prevent MS. In people who have MS, clinical trials show that taking vitamin D supplements does not keep symptoms from getting worse or coming back.
Vitamin D helps your body regulate blood sugar levels. However, clinical trials in people with and without diabetes show that supplemental vitamin D does not improve blood sugar levels, insulin resistance, or hemoglobin A1c levels (the average level of blood sugar over the past 3 months). Other studies show that vitamin D supplements don’t stop most people with prediabetes from developing diabetes.
Taking vitamin D supplements or eating foods that are rich in vitamin D does not help you lose weight.
Can vitamin D be harmful?
Yes, getting too much vitamin D can be harmful. Very high levels of vitamin D in your blood (greater than 375 nmol/L or 150 ng/mL) can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones. Extremely high levels of vitamin D can cause kidney failure, irregular heartbeat, and even death. High levels of vitamin D are almost always caused by consuming excessive amounts of vitamin D from dietary supplements. You cannot get too much vitamin D from sunshine because your skin limits the amount of vitamin D it makes.
The daily upper limits for vitamin D are listed below in micrograms (mcg) and international units (IU):