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Vitamin D3 (and K2)

By Jessica Seaton

Every few weeks a new study is released touting the benefits of vitamin D or pointing out that much of the world’s population is deficient in vitamin D. Both of these are true. Why has vitamin D become such a hot topic? And is this all just hype?

Vitamin D is really a prohormone, or precursor to a hormone, and not a vitamin, although it is called a vitamin. Vitamin D is known as the sunshine vitamin, and in fact, you can get adequate levels of vitamin D by being in the midday sun. However, an SPF 8 sunscreen blocks 95% of the UVB necessary for your body to make vitamin D. SPF 15 blocks 99% of the UVB. With the concern about sun-related skin cancers, we’ve created populations that are deficient in vitamin D. This deficiency has now been shown to be associated with breast cancer, colon cancer, prostate cancer, and ironically, melanoma, the most serious of all skin cancers. Melanoma usually occurs in areas that don’t receive much or any sun. Vitamin D can affect many organs and cause a variety of symptoms because every cell in the body has vitamin D receptors.

You may be wondering why all the hype now? In the 1920’s it was known that vitamin D was responsible for rickets in children and osteomalacia, a softening of the bone, in adults. The fact that vitamin D is a steroid hormone was not clarified until the 1930s. In the early 1970s Dr. Michael Holick isolated 25-hydroxyvitamin D3, the form that vitamin D takes as it travels through the blood, and in the late 1970s he isolated the active form of vitamin D3, 1,25-dihydroxyvitamin D3. Although much research has been done since then, many doctors are still unaware of the importance of vitamin D, or are resistant to recommending supplements and giving specific nutritional advice. This is unfortunate since research has shown that approximately 40% of the population has insufficient levels of vitamin D. Our indoor lives and copious use of sunscreen are probably the biggest culprits.

Vitamin D has been shown to be important in the prevention of osteoporosis, cardiovascular heart disease, type I diabetes, muscle and bone pain, fatigue, depression, hyperalgesia, autoimmune diseases (such as multiple sclerosis), and some cancers (breast cancer, colon cancer, prostate cancer). Other studies have shown:
  • a 61% decrease in the incidence of recurrent childhood wheezing was noted in children whose mothers had an intake of 724 IU of vitamin D during pregnancy. 2000 IU daily of Vitamin D given to children above the age of one showed an 80% decrease in type 1 diabetes.
  • both vitamin D and calcium were associated with a decrease in colorectal cancer.
  • supplemental or sunlight vitamin D was associated with a decrease in breast cancer. Low blood levels of vitamin D have been associated with increased risk of metastasis of breast cancer.
  • childhood sun exposure has been linked to reduced MS risk.
  • low levels of vitamin D are associated with tooth loss and poor dental health.

Vitamin D deficiency can cause muscle aches and weakness, bone pain, and fatigue. In the elderly individual muscle weakness combined with osteoporosis creates a high risk of a fall with hip fracture. Studies have shown that nursing home residents who were given vitamin D were subject to fewer falls. This effect is dose dependent: at 400 IU per day (the current RDA) there was no effect, but at 800 IU per day there was approximately a 25% decrease in hip and vertebral fractures. A relatively young USMS swimmer, Anna Lea Roof, wrote an article about her experience as a swimmer with vitamin D deficiency (http://www.usms.org/articles/articledisplay.php?a=152). After she was found vitamin D deficient, four months of high doses of vitamin D supplementation resulted in her being much stronger in the water not fatigued after a 90-minute workout.

When ultraviolet B is absorbed from the sun vitamin D3 (cholecalciferol) is created. It is transported to the liver where it is converted to 25-hydroxy Vitamin D. Later, the active form of vitamin D, 1,25-dihydroxy vitamin D is produced primarily in the kidneys, but also in the cells. Blood tests measure 25-hydroxy vitamin D, since that gives the most accurate picture of true vitamin D levels. People are considered vitamin D deficient if their 25-hydroxy levels are below 20 ng/mL (50 nmol/L). They are considered vitamin D insufficient with levels below 30 ng/mL (75 nmol/L) or 40 ng/mL (100 nmol/L). Optimal vitamin D status is between 40-65 ng/mL (100-160 nmol/L).

The best source for vitamin D is midday sun. If a light-skinned person goes outside in a bathing suit without sunscreen for ten or fifteen minutes he or she will get a dose of 20,000 IU of vitamin D. People of color doing the same thing may be getting only 4,000 IU of vitamin D and therefore need more sun exposure. To get enough vitamin D, a person should be exposed to the midday sun in a bathing suit, without sunscreen, three times per week. When exposing yourself to the sun, you should still put sunscreen on your face since the face is most often affected by skin cancer and does not generate that much vitamin D. You will also need sunscreen on your body with prolonged sun exposure, such as during swim meets. Even with adequate sun exposure, some people remain vitamin D deficient, particularly in winter, because of the angle of the sun, and the weather. It is very difficult to obtain enough vitamin D through food. Milk is fortified with 100 IU vitamin D per glass. Each 100 IU of vitamin D ingested raises the blood level by a mere 1 ng/mL. Oily fish is another source.

The most consistent way to get enough vitamin D is through supplementation. Ideally everyone would get tested to see what his or her blood levels are. Currently, this is one of the most ordered tests in the country. Based on those results, a very high dose of vitamin D, such as 50,000 IU a week for 8 weeks might be recommended. For those who do not have access to blood tests, a very safe dose would be between 1,000 and 4,000 IU of vitamin D per day. Even with sun exposure, this would not be too much. Toxicity is very rare. You can safely take 10,000 IU of vitamin D daily for five months and not have a problem. However, people with sarcoidosis, tuberculosis, histoplasmosis, Crohn’s disease, hypo- or hyperthyroidism, adrenal insufficiency, or who are taking thiazide diuretics should monitor their blood levels.

Supplemental vitamin D comes in two forms: vitamin D3 or cholecalciferol and vitamin D2 or ergocalciferol. While Dr. Holick believes there is no difference between the two, others consider cholecalciferol the more natural form to take since it is the form that our body produces.

Increased levels of vitamin D require increased levels of vitamin K, especially of vitamin K2 (menaquinone). Without enough vitamin K2 there is an increased risk of hardening of the arteries and other soft tissues. Vitamin K, along with vitamin D, are essential for the bones to uptake and incorporate calcium. Vitamin K is found in a soybean product called natto, and in broccoli, cabbage as well as in dairy products and egg yolks. Recommended daily intake is 120 mcg for adult men and 90 mcg for adult women.

Swimmers should be interested in vitamin D for several reasons. Since swimming is a non-weight-bearing sport, unless we supplement our swimming with a substantial amount of weight-bearing exercise, we are at risk for osteoporosis. Many of us already have osteopenia or osteoporosis. Vitamin D and vitamin K are necessary for the uptake of calcium in the bone. While taking calcium is important, vitamin D is just as important, if not more so.

Jessica Seaton, D.C. is a chiropractic orthopedist in private practice in West Los Angeles. In addition to sports medicine, she specializes in functional or alternative medicine with a nutrition emphasis. She has been swimming with West Hollywood Aquatics for over 18 years. She can be reached at or


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