Vitamin D and sport performance: more than just for bones

Vitamin D, otherwise known as the sunshine vitamin, is a fat-soluble vitamin that is derived from cholesterol and stored in fat. Vitamin D is well known to help us absorb calcium from the gut to promote bone development and growth. But more recent research indicates it has so many more functions for maintaining health and optimizing training and performance in athletes. 

It is now thought that athletes who have adequate (or higher) intakes and levels of vitamin D might increase skeletal muscle function; (mass, strength and endurance), decrease recovery time from training, increase both force and power production and improve immune function, each of which could enhance athletic performance. Vitamin D in its active form also acts like a steroid hormone, interacting with over 1000 genes throughout the body, serving nerve signaling and blood pressure.
 

VITAMIN D AND ATHLETIC PERFORMANCE

Bone Health Numerous studies have proven the positive influence of vitamin D on calcium and phosphate absorption in the gut and their impact on bone density and mineralization and remodeling.

Skeletal Muscle Function and Recovery Vitamin D can indirectly affect the recovery and construction of muscle tissue by stimulating contraction and the nervous system, thus reducing reaction time and improving balance and coordination of movement, (7, 8, 9). Vitamin D may also play a role in increasing testosterone and steroid hormones, leading to an increase in skeletal muscle hypertrophy, strength and power output.

Immune Function High training loads of athletes make them more susceptible to bacterial infections, (upper respiratory tract, cold, flu). Some studies have shown that by taking 2000 International Units (IU) daily of Vitamin D for one year can significantly decrease the incidence of common colds and flu.
 

ARE ATHLETES GETTING ENOUGH?

Simply put: NO! Vitamin D deficiency is on the rise throughout the world, surprisingly enough, 88.1 % of the world’ s population has inadequate vitamin D levels (16), particularly in the northern latitudes, where it can be hard to get enough sunshine, especially in the winter months. Reduced levels of vitamin D have been observed in athletes of various gender, age, and sport. Unlike other vitamins and minerals, only modest amounts of vitamin D come from food; (as seen in Table 1), instead, it is the sun’s ultraviolet B (UVB) rays that serve as our most efficient means of producing vitamin D. Therefore, athletes who train indoors or after sunset or who travel to foreign countries for training camps and competitions where dietary intakes of Vitamin D may be limited, may be at risk for Vitamin D deficiency. Severe, chronic vitamin D deficiency can lead to rickets, softened/weak-end and bowed bones that occur in children and adults, respectively.

Other factors that influence how much active vitamin D athletes can obtain from the sun include:

1. Time of year: vitamin D can only be synthesized when the sun is sufficiently high in the sky. For those living above 50° North, the sun’s zenith angle is low enough that vitamin D cannot be produced in the skin from October to early April.

2. Time of day: even during the peak summer season in Canada, UVB is only sufficient to produce vitamin D in the skin through the middle of the day, 11:00am-2:00 pm. This means that athletes training outdoors in the evening or early morning will likely produce little vitamin D, even on exposed skin.

3. Skin exposure: the most vitamin D is generated through UVB exposure on the torso, followed by the arms and legs, with the hands and face producing the least.

4. Skin pigmentation: individuals with darker skin have higher levels of melanin, which acts as a natural sunblock, slowing the production of vitamin D in theskin.

5. Altitude: UVB levels are higher at altitude than at sea level.

6. Sunscreen: blocks 95-100% of vitamin D production.

7. Cloud: complete cloud cover reduces UV levels by about half.

8. Shade & severe pollution: reduce UV by about 60%.

9. Glass: blocks UVB rays, so athletes who train indoors, even if they are exposed to daylight, will not produce vitamin D.

TABLE 1: Vitamin D Content and Some Common Foods (Canadian Nutrient File, 2015)

Vitamin D is not found naturally in many commonly consumed foods. In Canada, some foods such as milk, soy or rice beverages and margarine have vitamin D added to them. Good food sources of vitamin D include certain kinds of fish, egg yolks and milk. The following table will show you foods that are a source of vitamin D.

HOW MUCH IS ENOUGH?

The optimal dosage varies depending on the individual and the institution providing the guidelines in order to recap the above-mentioned performance benefits. Table 2 represents the recommendations of the Institute of Medicine (IOM), while the Endocrine Society (ES) recommends a slightly higher intake. Various organizations differ in what they determine is the lowest desirable serum level of Vitamin D in order to achieve full health benefits (17, 18, 19).

How Much Vitamin D Should Athletes Aim For?

Table 2: Recommended Dietary Allowances for Vitamin D (Institute of Medicine, 2010)*

ARE VITAMIN D SUPPLMENTS NEEDED FOR ATHLETES?

Vitamin D supplementation can be considered safe and appropriate for athletes who have low blood levels of vitamin D. Although exact levels are currently undetermined, it is suggested to be higher than general standards. In the absence of available screening and monitoring (e.g. blood work), a routine vitamin D supplement of 1000 IU of vitamin D per day may be considered safe and reasonable for all athletes. However, performance studies done on athletes were supplemented with 5000 IUs/day which is far greater than the recommended dosages of 600– 2000 IU/day. Thus, it remains unclear, but athletes may benefit from higher levels of Vitamin D than current recommended daily intakes in order to increase skeletal muscle function and reduce the risk of stress fractures.
 

VITAMIN D TYPES

There are two major forms of Vitamin D; D3 (cholecalciferol) and D2 (ergocalciferol). Vitamin D2 is mainly used in the fortification of foods, and is absorbed lower than vitamin D3. Vitamin D3 is made in the skin and found naturally in foods.

Commercial supplements can be in either form, however, Vitamin D3 may be the more effective.
 

BOTTOM LINE

Given the outlined numerous benefits of adequate Vitamin D to an athletes’ health, training and performance, it is important for athletes to get their Vitamin D status checked regularly during training. Parents and coaches can encourage more Vitamin D foods consumption to reap the sport performance benefits. However, in order to achieve optimal levels of Vitamin D, athletes who are at risk or who have below desirable levels (actual amounts are under review) (3, 18) may still need additional Vitamin D supplementation especially during winter months. More research is needed in athlete specific situations to determine optimal amounts of supplementation for its potential ergogenic benefits, but growing evidence has supported that 600– 800 IU/day may not be sufficient for optimal levels of vitamin D, in athletic population.

By: Angela Dufour, MEd, RD, CSSD, IOC Dip Sports Nutr, CFE Performance Dietitian for the 2018 Winter Olympics Article orginally published on www.coach.ca. as part of Coaches Plan – Expert Insight for Canada’s Coaches.