Vitamin D, also called the sunshine vitamin, keeps bones, muscles and immune system healthy. It regulates calcium and phosphate, helps with absorption of these minerals and influences genes that control cell growth and movement.
Darker skin can limit our ability to make vitamin D from sunlight and levels decline with age. Certain health conditions and medications can also lower vitamin D levels.
Bone Health
Vitamin D supports bone health, as it helps the body absorb calcium. It also regulates many other cellular functions and has anti-inflammatory and neuroprotective properties. Vitamin D is not naturally found in many foods, but can be absorbed through the skin via sunlight. It is also available in dietary supplements and fortified foods, such as milk and cereal.
Insufficient intake of vitamin D results in the classical deficiency diseases such as rickets in children and osteomalacia in adults and leads to weakened bones with increased fracture risk. Several clinical trials show that vitamin D and calcium supplementation improves bone health and decreases fracture risk in the elderly.
Optimal serum concentrations of 25(OH)D (also called calcium-difference hormone or calcitriol) are needed for optimal bone and overall health [2]. Serum 25(OH)D levels can be measured by laboratory tests. These lab tests measure the amount of active vitamin D in your body, a form known as 25-hydroxyvitamin D or 25(OH)D, and are reported in either nanomoles per liter (nmol/L) or micrograms per milliliter (ng/mL). A normal serum level is 50 ng/mL or more.
Immune Boost
Vitamin D supports the immune system and overall wellness. It helps regulate the renin-angiotensin-aldosterone system (and blood pressure), promotes cell growth, and influences the inflammatory and fibrotic pathways that contribute to cardiovascular disease. It also helps prevent depression and improves mental health. Vitamin D deficiency is associated with a higher risk for MS, an autoimmune disorder that causes damage to the myelin sheath that surrounds and protects nerve cells in the brain and spinal cord.
Individuals who do not eat enough vitamin D-fortified foods or who do not spend adequate time in the sun may be at risk for deficiency. Fat malabsorption due to conditions such as cystic fibrosis, Crohn’s disease, and celiac disease can interfere with vitamin D absorption.
Older adults may also be at increased risk of deficiency. People with darker skin produce less vitamin D in response to sunlight because their melanin pigment reduces the skin’s ability to absorb UVB rays. Additionally, obesity can interfere with vitamin D absorption because excess weight slows the movement of fat into the intestines, where it is absorbed. In a large, long-term clinical trial, supplemental vitamin D and calcium did not reduce cancer incidence or mortality in postmenopausal women. [93] However, further research is needed to determine whether vitamin D and calcium supplementation may help prevent cancer in other populations.
Vital Insights
The vitamin D metabolite 1,25(OH)2D regulates the activity of many genes that control cell growth and differentiation, as well as inflammatory processes. It is important for bone health, but it also may play a role in diabetes, depression, immune function and multiple sclerosis.
The committee that established the DRIs found insufficient or contradictory evidence linking vitamin D and a long list of potential health outcomes, except for bone health. However, research does suggest that vitamin D inadequacy may increase cancer risk and that adequate levels of 25(OH)D might decrease overall cancer mortality rates.
The USPSTF recommends that people who are not able to obtain enough vitamin D from diet alone take 10 mcg (400 IU)/day of supplemental vitamin D for the prevention of disease. Milk, orange juice, yogurt, some cheeses and fortified breakfast cereals are good sources of vitamin D. Supplements are available in drops, pills and creams. Talk to your doctor before taking vitamin D because high doses can cause nausea, vomiting and diarrhea. Vitamin D interacts with certain medications, including some anticonvulsants, antifungals and blood thinners. These medicines can reduce the absorption of vitamin D, leading to lower levels in the body. Discuss your use of these and other prescription and over-the-counter medications with your doctor.