Vitamin D is actually more a steroidal hormone than a typical vitamin. Among it primary functions is to aid intestinal absorption of calcium, magnesium, iron, phosphate and zinc. This action is responsible for vitamin D's reputation in the building and maintenance of strong and healthy bones. It is however also involved in countless essential body processes by influencing and signaling several thousand of the body's genes, synthesizing proteins and hormones, modulating immune and inflammatory responses, synthesizing new cells and recycling old ones. It is also involved in the production of glutathione, the body's master antioxidant. Cells require vitamin D to properly respond to pathologic and physiologic conditions. Vitamin D also influences skeletal muscle function. Adequate vitamin D has been shown to be preventative of numerous chronic diseases.
Strong correlations have been made between adequate vitamin D levels and optimal muscle function. Emerging evidence indicates a role in injury prevention, decreased recovery time from exercise, muscle growth, force and power production. Improving vitamin D levels has been shown to decrease pain and inflammation from sports injuries, and increase muscle protein synthesis, strength, jump velocity, jump height and power, physical performance and exercise capacity. Many athletically beneficial effects have been reported with as little as a single dose of ultraviolet light exposure.
This powerful vitamin/steroid/hormone is unfortunately in short supply in the average athlete. The prevalence of vitamin D insufficiency has increased significantly over the past 3 decades and is now thought to be a staggering 77% of the general population. Some estimates go as high as 85%. Similar rates are found among athletes in general but even higher numbers of indoor athletes are affected. Vitamin D deficiency diminishes calcium absorption and can lead to decreased bone density thereby increasing the risk of fracture, including stress fractures. Bone remodeling following fracture is also impaired by low vitamin D as is immune response and the myriad of other processes highlighted above. These can all affect the training athlete and their performance levels.
Athletes are at risk of low vitamin D for a few reasons. Most don't consume appreciable amounts of vitamin D rich foods. It is difficult for anyone, maybe impossible, to maintain adequate levels of D from foods alone. Secondly, many don't supplement, or test to assess their levels. Many are also overly cautious of sunlight exposure and don't find a balance with a healthy level of UVB ultraviolet light required to convert cholesterol in the skin to vitamin D. Vitamin D production is prevented with the use of sunscreens, avoiding peak midday sunlight hours and over dressing. While it is advisable not to burn, one should seek sub-burn exposures of 15-20 minutes, (more or less depending on pigmentation and individual burn tendencies, burn history, and familial predilections to skin cancers) a few times a week at least during high sunlight intense seasons, to maintain healthy levels. Depending on latitude, many athletes will need to supplement in winter months and early spring months to keep those optimal levels.
There are two forms of vitamin D which are important to humans, Vitamin D2 (ergocalciferol) and D3 (cholecalciferol). Vitamin D2 is produced by certain plants and mushrooms. Many fortified foods such as milk, grains and cereals and some high dose prescription supplements use D2 as an inexpensive way to increase nutrient content. There is however a big difference between D2 and D3 and they should not be confused. Vitamin D3, which is found in animal products such as cod liver oil, other oily fish such as salmon, tuna, mackerel, sardines, egg yolks and D3 supplements, is much more bioavailable, and more easily absorbed. It is also more easily converted in the liver into the bioactive form of vitamin D which is more readily converted to its hormone form in the kidneys. Our bodies can synthesize vitamin D3, in good quantities, from the photo-transformation of cholesterol in the skin. This process requires adequate exposure to UVB rays in sunlight or from artificial light sources.
The Institute of Medicine(IOM) recommendations for dietary intake of vitamin D were updated in 2010 to 400-600 IU per day for children and adults and 800 IU per day for those over 70 years old. They set their safe upper limit of intake from 9 years old and up, at 4000 IU per day. Since their release, these values have been controversial with many experts arguing that they are grossly inadequate for preservation of bone health, reduction of falls, fracture risk and vitamin D's many other roles. The Endocrine Society pegs their recommendations at up to 1000 IU per day for children up to 18 years old and up to 2000 IU per day in adults in addition to adequate sun exposure. They set their upper limit at 10,000 IU per day. Recent research has found the relative toxicity of vitamin D to be low, even at doses of 30,000 IU for extended periods and there is no known toxic limit to the vitamin D produced in the body from sun exposure. Recently, researchers at the University of California, San Diego and Creighton University have uncovered an error in the calculations used by IOM in formulating their recommendations. They published a letter in the journal Nutrients in 2015, stipulating that their research shows the IOM recommendations to be about a tenth of the actual body requirements of vitamin D. They recommend a minimum of 7000 IU of vitamin D per day from all sources. Keep in mind, that during peak sunlight hours of 10AM to 3PM in the months when sunlight contains adequate UVB radiation, 15-20 minutes of unprotected sunlight exposure can yield over 10,000 IU of vitamin D in light skinned people.
How we assess Vitamin D levels:
serum 25-hydroxyvitamin D or 25(OH)D Optimal level is 50-100ng/mL with a super optimum level of 70-80 ng/mL
The RunTheLabs Optimum range for vitamin D is a 25(OH)D level from 50-100 ng/mL with a narrower super optimum of 70-80 ng/mL. Levels over 40ng/ml are required to prevent fractures and there is some evidence that levels around 50ng/mL are associated with peak neuromuscular function. Insufficiency and excess (levels above 125 ng/mL) vitamin D alike are associated with increased overall health risk from all causes. Above 150 ng/mL symptoms such as hypercalcemia can occur. Though rare, Vitamin D toxicity can cause significant mineral imbalances, especially of calcium and phosphorus, fatigue, nausea and vomiting, constipation, confusion and forgetfulness.
Generally, when individuals have optimized their diets to include more naturally occurring vitamin D and have made efforts to optimize sunlight (UVB) exposure their numbers will improve. Often, however, supplementation is needed to achieve optimum levels. The supplemental form of choice is vitamin D3 and there are many good products on the market from liquids, to tablets, capsules and sublinguals. Another good way to supplement vitamin D is with a quality cod liver oil. Cod liver oil contains over 1300 IU in a teaspoon and also provides anti-inflammatory Omega 3 fats and vitamin A. Vegans and vegetarians, take note that much of the D3 on the market is derived from lanolin a waxy substance sourced from sheep's wool. We advise you to do your research in selecting a product as their seems to be much confusion in the industry and with labeling. Vitashine has a D3 product that it derives from lichen and could be a suitable choice.
When levels are deficient, below 20ng/mL we recommend taking 10,000 IU of D3 for 10 days, then 5000 IU per day until retesting in 6-8 weeks from initial testing for those 12 years old and up. For levels of 30 to 40 ng/mL, we recommend 5000 IUs until retesting confirms optimized levels. At 40 to 49 IU, we recommend to just begin taking 5000 IU per day until optimum levels are reached. One can make sensible adjustments to dosages if levels are stubborn to move up or conversely if they move rapidly to optimum ranges. Some will maintain optimum levels with as little as 1000 to 2000 IU per day. Children can safely take about 1000 IU for every 25 lbs of body weight. Vitamin D is fat soluble so absorption is best taken at or close to meals that contain fats. The same is true for the vitamin K mentioned below.
Recently, evidence is mounting that another vitamin partners synergistically in several of vitamin D's chief roles. Vitamin K is often thought of for its role in healthy blood clotting functioning. Most know this vitamin, in its K1 form, can be found in certain foods like leafy greens. Vitamin K, specifically K2, and a particular form of K2 known as mk7 has been shown to be key to optimum bone health and reduction in chronic disease risk such as coronary vascular disease. One of the major roles it is shown to perform is as vitamin D aids in mineral, and notably calcium absorption in the gut, it is K2 that directs this calcium into bones thus keeping it where we want it. This helps promote skeletal integrity, and bone strength preventing fractures, and keeps calcium from where it can do harm such as in plaque buildup in arteries or in deposits in organs, joints and soft tissues.
Though there is no accurate way to measure vitamin K levels in the body, many researchers feel the majority of the populous has insufficient amounts of vitamin K. Optimal intake has been suggested at 100-200 mcg of K2 (mk7 form) per day for every 5000-10,000 IU of vitamin D3 taken. RunTheLabs recommends supplementing at this range along with any D3 supplementation for reduction of fracture risk and overall significant health benefits associated with it. Note, these recommendations do not apply to anyone undergoing prescription anticoagulant therapy who are typically restricted from ingesting vitamin K rich foods and who should never consume any vitamin K containing product or supplement unless otherwise directed by their physician.
Coaches, trainers, and health care practitioners should recommend that athletes get their plasma 25(OH)D levels measured at least a couple times per year. Levels are generally lowest in early spring which makes this a good time to get a baseline, but anytime is a good time to assess for insufficiency. Those in more northerly latitudes should pay special attention to the seasonal influence of lower intensity sunlight during late fall and winter and try to optimize and maintain levels before they decline. With continual monitoring and adjusting of sunlight exposure and supplementation accordingly athletes can enjoy the multitude of overall health benefits attributed to vitamin D and it's related benefits to their athletic endeavors. Further studies are needed to flesh out the breadth of impact this important vitamin has on total athletic performance, but its impact on overall health and wellness makes it vital to the competitive athlete.