One of the most interesting sessions of the recent 2009 North American Menopause Society discussed the impact of Vitamin D on health issues important to women. Did you know that low levels of vitamin D have been linked to breast cancer, colon cancer, ovarian cancer, high blood pressure, and strokes? This is in addition to the well established role that vitamin D plays in bone health. Condensing the most current research down to a practical level let’s answer these questions:
• Is all Vitamin D the same?
• What are some common sources of Vitamin D?
• How much Vitamin D is recommended?
• How much of an impact does vitamin D have on female cancers?
• What about other health problems?
• Should I get my blood Vitamin D level tested?
Vitamin D from sunlight, foods, and even vitamin supplements is not biologically active. It has to undergo two processes, the first occurring in the liver which converts vitamin D to the 25(OH)D form, also known as calcidiol or Vitamin D². The kidney then makes the most active form 1,25(OH)²D, also known as calcitriol or Vitamin D³. If you check your bottle of vitamins, or calcium + vitamin D supplements, you can see which type you have been taking. Currently the preferred supplement form may be Vitamin D³ as it increases the amount of active Vitamin D while increasing the time Vitamin D is active in the blood and tissues.
Vitamin D is made when UV-B rays strike the skin. One general recommendation has been to have 20 minutes of sun exposure to face, arms, leg or back twice a week during the most intense times for sun exposure (i.e., 10:00 AM through 3:00 PM). Alas, the amount of Vitamin D that can be obtained this way can be limited by several factors. If one has dark skin, uses an 8 or greater SPF sunscreen, wears occlusive clothing, or gets sun exposure only through window glass-the amount of Vitamin D is greatly decreased. If one lives above the 42nd parallel, the months of November through February do not produce sufficient Vitamin D even when the sun is not hidden by clouds. Cloud cover, shade, and air pollution will further reduce the amount of UV-B.
Many of us prefer to get vitamins naturally from whole foods as opposed to supplements. Some of the highest sources of Vitamin D are listed below:
|Cod liver oil, 1 tablespoon||1360 IU|
|Cooked salmon, 3.5 ounces||400 IU|
|Sardines in oil, drained 1.75 ounces||250 IU|
|Tuna in oil, drained 3 ounces||200 IU|
|Vit D fortified orange juice, 1 cup||142 IU|
|Vit D fortified milk, 1 cup||98 IU|
|Vit D fortified yoghurts, 6 ounces||80 IU|
|Egg yolk, 1||20 IU|
For comparison, the usual amount of Vitamin D in a multivitamin pill is 400 IU (International Units).
Since the 1930′s, when milk was first fortified with vitamin D to prevent rickets, the usual recommendation has been 200 IU to 400 IU daily during times of inadequate sun exposure. Women above age 50 should be receiving 400 IU to 800 IU. Recently, experts in the area have been lobbying for a new recommended level of 1000 IU daily among adults (Vieth, 2007). The Food and Nutritional Board at the Institute of Medicine began reviewing the published studies in 2008 and are expected to publish new guidelines in spring of 2010.
For comparison, the upper tolerable limit (adverse results begin to appear) has been reputed to be 2000 IU/day. Many researchers in the field have suggested that the toxic level is closer to 10,000 IU/day over a more prolonged period of time.
Given what you now know about the different types of Vitamin D and the different amounts used by women you can appreciate the difficulties in trying to establish the clear cut role of Vitamin D in cancer prevention. In the most recent, largest study (meta-analysis) of Vitamin D, calcium and the prevention of breast cancer (Chen, 2009), both Vitamin D and calcium seemed to be protective for the development of breast cancer. The best results were among women with the highest intakes of Vitamin D and calcium as compared to the lowest levels of consumption. The top quarter of women having the highest blood 25(OH)D levels had a 45% decreased risk of breast cancer.
Another study of 562 women (Rejnmark, 2009) found that the 142 women with a diagnosed breast cancer had, on average, lower blood levels of 25(OH)D. Women with the highest levels of 25(OH)D had a significantly reduced risk for breast cancer. Surprisingly, use of Vitamin D supplements, sunbathing, and fish intake did increase blood levels of 25(OH)D-but the lifestyle factors did not directly impact the risk of breast cancer.
Conversely McCullough and colleagues (2009), studying almost 22,000 women, found no impact of blood levels of 25(OH)D on the risk of breast cancer. A study of almost 42,000 Swedish women (Kuper, 2009) did not identify linkages between breast cancer risk and sun exposure, nor Vitamin D intake through diet or multivitamin use.
The impact of Vitamin D on ovarian cancer has not been as well studied but it has been purported to have a protective effect. Researchers at the Channing Laboratory (associated with Harvard University) used data from four large studies to examine the effects of Vitamin D (Tworoger, 2009) on ovarian cancer. It was determined that blood levels of Vitamin D did not directly impact cancer risk from any of the four genotypes. However, a specific type of the Vitamin D receptor gene was significantly tied to ovarian cancer risk.
Several studies have found that blood levels of 25(OH)D could be predictive of colon cancer risk. More recently Ng (2009) and fellow investigators looked at both risk for getting colon cancer, and the ability to survive, as it related to 25(OH)D blood levels among 1017 persons. Participants in the top quarter of 25(OH)D levels, as opposed to the lowest quarter, had significantly less colon cancer. They also had the lowest death rates from colon cancer, and the lowest rates of over all mortality.
In Finland a 25-30 year study of over 6,000 persons found an increased risk of fatal vascular disease in those who had the lowest blood levels of 25(OH)D. Interestingly, this relationship was apparent for the incidence of strokes but not heart attacks (Kikkinen, 2009). Proposed mechanisms for improved blood vessel health include Vitamin D’s beneficial impact on high blood pressure via kidn
ey hormones, decreased inflammation inside the arteries, and improved insulin resistance via changes in parathyroid hormone (Lee, 2008).
There have been studies suggesting that high dose supplements of Vitamin D, or fish oil supplements, may improve mild depression. Jorde (2008) noted an improvement in scores on the Beck Depression Inventory after a year of supplementation with 20,000-40,000 IU per week of Vitamin D as compared to placebo. This was a study of overweight and obese subjects, not persons with diagnosed depression. At this point, treatment with high dose Vitamin D for depressive symptoms is considered experimental and should be considered only with medical supervision.
Systemic Lupus Erythematosus (SLE) & Rheumatoid Arthritis (RA)
Vitamin D has found to have effects on immune function and inflammation. Earlier studies suggested a relationship of Vitamin D to autoimmune conditions. A group of women within the Nurses Health Study was targeted with food and vitamin questionnaires. There was no apparent association between increasing Vitamin D intake and the risk of developing these autoimmune disorders (Costenbader, 2008).
As with many blood tests (e.g., hormone levels) there can be considerable variation in results from lab to lab, time of day or season (e.g., Vitamin D levels tend to be best at the end of summer). Perhaps the best indicator of general Vitamin D levels is 25(OH)D blood test for it measures Vitamin D from both sun and dietary sources. This form of Vitamin D also lasts in the body for around 30 days.
In many cases the “normal” or preventative level of Vitamin D has yet to be determined. Cardiovascular risk begins to rise steeply when the blood level of 25(OH)D is below 10-15 ng/mL. Optimal levels may be at least 30 ng/mL. Depending upon all other factors present it might take a daily intake of 1000-2000 IU per day get to blood levels of 30 ng/mL (Giovannucci, 2009). The following blood 25(OH)D levels are taken from an updated National Institutes of Health document:
|Blood level||Health Status|
|<10-15||<25-37||Consistent with rickets, low bone density, poor health|
|>15||>37.5||Adequate for healthy persons|
Some Vitamin D researchers have stated that most benefits level out at blood levels of 30-40 ng/mL (Giovannucci, NAMS 2009). It will remain to be seen if the new recommendations due to be published in May of 2010 will have different cut off levels for defining optimal blood levels.
So, who should push for blood testing? Bearing in mind that the 25(OH)D blood test can cost upwards of $200, many primary care providers have chosen to just recommend an increased intake of Vitamin D. The dose is based upon the person’s specific health history. Until there are studies set specifically to establish optimal dosage and blood levels the primary care model makes sense. Among healthy adult women, without excessive sun contact, consuming 800 IU per day of Vitamin D is a reasonable choice. For your specific Vitamin D recommendation, check with your GYN or primary care provider.
If you are interested in more information, the National Institutes of Health site offers an excellent overview, especially of the effects of Vitamin D on specific health conditions:
Stay tuned for a discussion of the newest recommendations when they are released!