The Role of Vitamin D in Osteoporosis

Vitamin D is most well-known for the role it plays in supporting bone health. Vitamin D helps the body absorb calcium and phosphorus, crucial elements for maintaining strong bones. Calcitriol, the active form of vitamin D, stimulates and controls active calcium absorption in the intestines. If the body has low levels of vitamin D, it is less able to actively absorb calcium from the gut.  

The concept of vitamin D was first described during industrialization in the 1800s. It was observed that children living in cities were much more likely to develop rickets, a condition that causes softening and weakening of bones, than children living in rural areas. It was proposed that this difference between urban and rural children was due to differences in sun exposure. Children living in cities often spent more time indoors and lived in buildings that were close together and did not allow much light in. Eventually, it was shown that increasing sun exposure of children with rickets remarkably improved their condition. From these observations, it was determined that sun exposure must lead to something being made in the skin that improves bone health. This new discovery was named “Vitamin D”.[1] 

Despite its name, vitamin D is not a vitamin. Vitamins are micronutrients that are essential for supporting health and must be obtained through diet because they cannot be made by the body. Vitamin D is actually a pro-steroid hormone that is made in the body when the skin is exposed to ultraviolet B (UVB) light from the sun. 

Osteoporosis is the thinning of bone tissue and loss of bone density over time. Bone tissue is constantly broken down and replaced by the body. Osteoporosis occurs when the body fails to form enough new bone to replace the loss of old bone 

The best way to prevent osteoporosis is to make long-term choices that keep your bones healthy throughout your life. Calcium is one of the most important nutrients for supporting bone health and facilitating new bone growth. In order to prevent osteoporosis, it is critical to get enough calcium in your diet and have high enough vitamin D levels that this calcium can be absorbed by the body.  

Does vitamin D deficiency cause osteoporosis?

Osteoporosis causes bones to become weak and brittle, increasing the risk of fractures. Those diagnosed with osteoporosis are nearly five times more likely to experience a hip fracture, resulting in three times greater one year mortality risk.[2] In the United States, osteoporosis is responsible for approximately 1.5 million fractures and 500,000 hospitalizations annually.[3,4] 

A variety of factors can put an individual at risk of developing osteoporosis. Autoimmune, gastrointestinal, nervous system, and hormonal disorders can all increase likelihood of osteoporosis.[5] 

Many studies have found a link between low vitamin D and osteoporosis and suggest that having a low level of vitamin D is a risk factor for developing osteoporosis. Vitamin D impacts calcium metabolism, bone remodeling, and bone density, all of which are important factors for preventing osteoporosis.[6] Vitamin D insufficiency is highly prevalent among those with osteoporosis and research shows a lack of vitamin D is associated with low bone mineral density and increased fracture risk.[7-11] 

Can vitamin D stop osteoporosis?

Studies have shown that vitamin D can help with osteoporosis prevention and is inversely related to the severity and progression of the disease.[10, 12-17] 

A meta-analysis of several randomized placebo-controlled trials found that supplementation with at least 800 International Units (IU) of vitamin D led to a 30% decrease in hip or non-vertebral fractures compared to the placebo.[12] Another study that looked at the impact of vitamin D on bone mineral density found that over 80% of subjects with vitamin D insufficiency and all subjects with vitamin D deficiency had low bone mineral density.[8] This study highlights the importance of vitamin D for the maintenance of healthy bones and management of low bone mass. 

Treatment recommendations for osteoporosis often include medications called bisphosphonates which stop or slow down bone breakdown, preserve bone mass and increase bone density.[17] It has been demonstrated that adding vitamin D to traditional osteoporosis drug therapy treatment can improve bone mineral density and fracture risk.[18-20] 

Does calcium and vitamin D help osteoporosis?

Since low vitamin D is a risk factor for osteoporosis, it is important that those with and at risk for osteoporosis take steps to maintain a sufficient vitamin D level. Vitamin D and osteoporosis research indicates that 30 ng/mL is the minimum vitamin D level required to see a decreased risk of bone fracture.[12] 30 ng/mL is also the minimum threshold for being considered vitamin D sufficient. Those with levels between 20-29 ng/mL are considered insufficient and levels below 20 ng/mL are vitamin D deficient. Therefore, osteoporosis patients should aim to maintain vitamin D sufficiency. 

Vitamin D is naturally produced in the body when the skin is exposed to sunlight but getting enough vitamin D from sun exposure for osteoporosis can be tricky. Recommendations vary, but in order to maintain a healthy vitamin D level from the sun, a person needs to be outside for approximately 15 minutes at mid-day, multiple times per week. At northern latitudes, it is impossible to make vitamin D outside between October and May due to the angle of the sun. This has led many to turn to dietary sources for vitamin D. Vitamin D is naturally present in very few food sources, so supplements are the main form of dietary intake. Calcium supplements are also commonly recommended for helping treat osteoporosis. 

Among the medical community, there is debate around the recommended dose of vitamin D and calcium supplements for preventing osteoporosis. The Institute of Medicine’s (IOM) recommended dietary allowance for vitamin D is 600 IU per day. Many vitamin D researchers disagree with this recommendation and say that the IOM’s recommended allowance is not enough to prevent deficiency or support bone health. The National Osteoporosis Foundation’s vitamin D dosage guidelines for osteoporosis range between 400 and 1000 IU per day but notes that some people may need more than this. They also recommend between 1,000 and 1,200 mg of calcium daily.[21] 

Generally, 4,000 IU of vitamin D or less per day is considered safe, as long as your blood values are being monitored. It is important to avoid excessive doses of oral vitamin D. If vitamin D intake is too high, it can cause vitamin D toxicity and potentially dangerous consequences.

Obtaining vitamin D from light allows your body to self-regulate vitamin D production and make as much as it needs to stay healthy, without any risk of overdose or toxicity. Unlike with oral supplements, you cannot overdose on vitamin D3 produced by your skin. If you have enough vitamin D, your body will simply produce less.