Vitamin D, long touted for its ability to work with calcium to preserve bone health, is more than a one-trick pony. The sunshine vitamin, so named because the best source is the vitamin D your skin produces in response to sunlight, plays a key role in health. Because not everyone gets enough sunlight and vitamin D isn’t abundant in most foods, vitamin D deficiency is an issue for some people. According to Medscape.com, almost two-thirds of adults in Boston are vitamin D deficient by winter’s end due to lack of sun exposure.
It’s clear that we need more focus on optimizing vitamin D. Keeping your vitamin D level from falling too low may have benefits that extend beyond bone health. A study carried out by researchers in the Netherlands found that adults with low levels of vitamin D were at a 35% higher risk of developing cardiovascular disease and 14% more likely to develop cancer. Their risk of mortality was also higher overall.
Why is vitamin D so important? Beyond bone health, D vitamin helps regulate the immune system. How your immune system responds to your environment is key to good health. You want optimal immune health to fight foreign invaders, like bacteria, viruses, and tumor cells, while not being so aggressive that it damages healthy tissues. However, vitamin D may also play a role in physical fitness. Let’s look at how vitamin D might affect your fitness level and your sports and training performance.
Does Vitamin D Affect Aerobic Capacity?
One of the best measures of cardiorespiratory fitness is aerobic capacity, the efficiency with which your heart and lungs can deliver oxygen to tissue, and how efficiently your tissues can use that oxygen. Better aerobic capacity (V02max) is linked with greater endurance during sub-maximal exercise and greater longevity.
What is the link between aerobic capacity and vitamin D? In the study, researchers found subjects with a higher vitamin D level had a higher aerobic capacity than those who had lower vitamin D levels. However, this study only shows a correlation between the two and doesn’t necessarily show causation. It’s not clear whether vitamin D itself improves aerobic capacity and cardiovascular fitness or whether some other factor common to people with a higher vitamin D level is the reason.
For example, people with greater aerobic capacity may spend more time outdoors in the sun where they synthesize more vitamin D. They may also be more health-conscious and more likely to take vitamin D supplements.
Yet muscles have receptors for vitamin D on their surface, and studies show that low vitamin D increases oxidative stress and affects the activity of antioxidant enzymes within muscles. Therefore, a deficiency could affect aerobic capacity by allowing oxidative stress to muscle tissue to go unchecked.
Another study found that men and women who had a vitamin D level in the highest quartile had 4.3 times greater aerobic capacity relative to the lowest quartile. As one of the study’s authors, Amr Marawan, MD points out, the study doesn’t show cause and effect but the findings were “strong, incremental, and consistent” across groups.
Muscle Strength
Does vitamin D affect muscle strength too? As mentioned, muscles have receptors for vitamin D on their surface. Some studies show that people with a low level of vitamin D performed less well on tests that require muscle strength, but most of the subjects were elderly. The question is whether consuming more vitamin D improves strength. Research shows women with more muscle mass have higher levels of active D, and researchers believe that vitamin D may play a role in muscle strength. However, the correlation is weaker between muscle strength and vitamin D in men.
A 2017 study of young, middle-aged, and older men and women found those with higher vitamin D levels had greater upper and lower body strength. Other research links a higher vitamin D level with greater strength and power in the legs. This is an area that needs more research, but there is some evidence that keeping your vitamin D level in the optimal range might improve strength-training performance.
How low is too low? While a vitamin D level of 20 nmol/L or higher is considered normal, many experts believe the optimal level is higher. In terms of muscle strength, most of the research suggests that 50 nmol/L helps optimize muscle strength. If you’re low, ask your physician how much vitamin D you should take daily to bring it into a healthier range. It’s important not to take mega-doses of vitamin D since your body stores the excess and can’t eliminate it. Too much vitamin D can be toxic.
The Bottom Line
Vitamin D is important for bone health and the health of your immune system but it may also impact facets of fitness too such as strength and aerobic capacity. That’s why you don’t want to be deficient. People at higher risk of vitamin D deficiency include:
- The elderly
- Those who are obese
- People with medical conditions that affect vitamin D absorption, such as celiac disease
- Darker-skinned people
- Those who live in Northern latitudes
- Those who get little sun exposure
- People with liver or kidney conditions
If you fall into one of these high-risk groups, ask your physician to check a vitamin D level to see where you stand. It’s safe for most people to take 2,000 IU of vitamin D daily and most experts believe up to 4,000 IU each day is safe. According to the Institute of Medicine, 4,000 IU daily is the safe upper limit. If you take more than that, it’s important to monitor your level to ensure it doesn’t rise too much and you shouldn’t take more than the upper limit unless you’re deficient. Talk to your physician about what is best for you.
References:
- Harvard T.H. Chan School of Public Health. “Vitamin D”
- com. “High Vitamin D Levels Linked with Better Fitness”
- Ther Adv Chronic Dis. 2011 Jan; 2(1): 25–37.doi: 10.1177/2040622310381934
- Eur J Appl Physiol. 2019; 119(4): 825–839.Published online 2019 Mar 4. doi: 10.1007/s00421-019-04104-x.
- J Clin Endocrinol Metab. 2012 Dec; 97(12): 4366–4369.doi: 10.1210/jc.2012-3720.
- “High levels of vitamin D may improve muscle strength”
- com. “Vitamin D: Vital Role in Your Health”
- Medicine Science Sports Exercise. 45: 157-162, 2012.
- com. “High Vitamin D Levels Are Linked to Better Exercise Capacity”
- J Hum Nutr Diet. 28, 636–645 doi:10.1111/jhn.12268.
- com. “What is the prevalence of vitamin D deficiency in the US?”
- com. “At what dose is vitamin D toxic?”
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