3 Reasons Why You Need Vitamin D

Dark mornings and early sunsets aren’t just reminders that fall and winter are coming. They also mean it’s time to rebuild vitamin D levels. Because sun exposure is a critical part of getting enough vitamin D, it’s common for levels to drop during fall and winter months, leading to greater risk for health complications.

It’s fairly well known that vitamin D (along with calcium) is important for bone health for both adults and kids. In fact, a recent clinical report from the American Academy of Pediatrics emphasized the importance of kids getting enough calcium- and vitamin D-rich foods to establish a foundation for healthy bone development and maintenance (1).

But vitamin D influences much more than the skeletal system. Because it acts more as a systemic hormone than simply a vitamin, the nutrient has been the subject of continuing research over the last decades.

The evidence suggests three new reasons for making vitamin D a priority now that levels are plummeting for most the population:

1. Recover faster after exercise.

The day after a hard workout can be painful. Feelings of soreness, stiffness, and fatigue will undeniably affect performing the days following. Avoiding this situation may be as easy as making sure to have adequate amounts of vitamin D. A study found that subjects with pre-existing low vitamin D levels had significantly more exercise-induced muscle weakness compared to those with adequate vitamin D levels (2).

Getting the right kind of vitamin D can be important, too. In a study published in Nutrients, athletes who took vitamin D in the form of D2 (ergocalciferol), rather than D3 (cholecalciferol), actually had worsened muscle damage and delayed recovery after intense workouts when compared to a placebo (3).

2. Keep arteries healthy.

Arterial health directly contributes to heart health along with other factors such as diet, weight, and stress. Scientific literature increasingly supports the link between vitamin D inadequacy and poor arterial health.

One of the reasons may be that vitamin D is necessary for blood vessels to maintain their normal function and flexibility. Arteries are blood vessels that act like highways in our bodies, delivering oxygen and vital nutrients to various organs. Over time, aging as well as lifestyle and dietary factors can cause arteries to stiffen, lose their flexibility, and even harden, ultimately increasing cardiovascular risk.

A simple way to help avoid this fate is by getting enough vitamin D. A recent cross-sectional analysis with more than 1200 subjects found lower vitamin D levels was associated with increased arterial stiffness (4). While the exact mechanism is unknown, research for vitamin D being a key to heart health is strengthening.

3. Support to the immune system.

In addition to shorter days, the change of seasons means more work for the immune system. It’s the annual time when new, unrecognized pathogens quickly spread from person to person. Washing hands, getting vaccinated, and avoiding those that are sick all help prevent contracting illness. Vitamin D won’t prevent infection, but recent research suggests that it’s necessary for keeping the immune system in proper functioning order.

Signifying the importance of the hormone-like vitamin is the discovery that immune cells (B cells and T cells) have vitamin D receptors that directly contribute to regulating immune response (5). This may help explain why older adults who are especially susceptible to low vitamin D levels because of more time spent indoors have more suppressed immune systems in winter months, according to a study in the Journal of Endocrinology and Metabolism (6).

Normally, spending a little more time in the sun would help boost vitamin D levels to where they should be. However, the fall and winter seasons offer weak exposure to the UVB rays needed to produce vital vitamin D (depending on latitude, clothing worn, and amount of time spent indoors). Additionally, not many foods supply enough vitamin D to meet recommended intakes of 800 IU per day—an amount that has been debated to be sufficient but not optimal for health.

In the colder months, vitamin D experts agree that supplementation is the best course of action to stay healthy. The latest recommendations are to get at least 2000 IU of vitamin D (preferably in the more bioavailable form for D3, not D2) to maintain healthy blood levels.


Golden NH, Abrams, SA, et al. Optimizing bone health in children and adolescents. Pediatrics2014;143(4):e1229-e1243.
Baker T, Henriksen VT, Martins TB, et al. Higher serum 25-hydroxyvitamin D concentrations associate with a faster recovery of skeletal muscle strength after muscular injury. Nutrients2013;5(4):1253-75.
Cannell JJ, Hollis BW, Sorenson MB, et al. Athletic performance and vitamin D. Med Sci Sports Exerc 2009;41:1102-10.
Giallauria F et al. Arterial stiffness and vitamin D levels: the Baltimore longitudinal study of aging. J Clin Endocrinol Metab 2012;97:3717-23.
Aranow C. Vitamin D and the immune system. J Investig Med 2011;59(6):881-6.
Laird E, McNulty H, Ward M. Vitamin D deficiency is associated with inflammation in older Irish adults. J Clin Endocinol Metab 2014;99(5):1807-15.