Vitamin D is a fat-soluble vitamin that works with calcium to build and maintain healthy bones. It also plays a role in many other cellular functions throughout the body including immune health, muscle function and brain cell activity.

It's essential for good bone health, but if you don't get enough of this vital vitamin through your diet, you can benefit from supplementation to ensure you have optimal levels. The best way to get your daily dose of vitamin d is through sunlight, fortified foods and supplements.

Sun exposure converts a chemical called calciferol into vitamin D2 and vitamin D3. You can naturally make your own vitamin D through a few things: sunscreen, eating foods rich in omega-3 fatty acids, and taking cod liver oil supplements.

You can also find vitamin D in a number of fortified foods including milk, cereals and fatty fish such as salmon and mackerel. However, if you have certain medical conditions or take medications that affect your body's ability to absorb vitamin D, you may want to speak with your doctor about a supplement.

There are several different forms of vitamin D, which include vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). In some cases, it's difficult to convert sunlight into ergocalciferol in the body, so you may need a supplement to make sure you have adequate levels.

Although there are some positive effects associated with high-dose vitamin D supplements, the results of clinical trials have been mixed. In one study, for example, a high-dose vitamin D3 supplement (800 IU per day) did not improve lower extremity strength and performance in older adults. In another, a high-dose vitamin D3 (600 IU per day) did not improve upper-extremity strength and performance in frail and elderly patients.

In addition, a large, multi-center, randomized controlled trial found that supplemental vitamin D3 did not reduce the risk of cardiovascular disease (CVD) in elderly women. Despite this, some observational studies have linked lower serum 25-hydroxyvitamin D (25(OH)D) concentrations to an increased risk of CVD, although these relationships were not statistically significant [93].

Besides its role in bone and overall health, vitamin D plays a crucial role in your immune system by supporting T cells, the body's white blood cells that fight infections. It also helps regulate the renin-angiotensin-aldosterone system, a hormonal balance that affects blood pressure and vascular function.

It also reduces the risk of cancer and has anti-inflammatory properties. Some evidence suggests that supplementation of vitamin D3 reduces the incidence of colorectal, breast, lung, and pancreatic cancers. A meta-analysis of prospective studies, which included 16 trials, found that higher serum 25(OH)D levels were associated with a lower rate of these cancers [89].

While it's easy to find vitamin D in fortified foods, many people lack sufficient sun exposure or don't eat a wide variety of foods containing vitamin D. This is why so many people are deficient in this nutrient, and why it's important to be aware of your intake and how to optimize your levels.