The trouble with vitamin D

We all know that vitamin D is a necessary fat soluble vitamin that is synthesized in the skin in response to sunlight and is in a few foods.  The best natural food sources are fatty fish such as salmon, tuna and mackerel with only small amounts in egg yolks, cheese and beef liver.  Many foods are fortified with vitamin D.  Milk is usually fortified, but products made form milk may not be, so we have to read the label.  Mushrooms may have the vitamin D content enhanced by exposure to ultraviolet light.  Most people get vitamin D from supplements.  In fact, the Nutrition Business Journal reported that sales are significantly up: from $50 million in 2005 to $550 million in 2010.


The essential role of vitamin D in skeletal health is likewise well known, but what about the non-bone and particularly breast cancer benefits.


Much of our information about the health effects of vitamin D comes from population-based observation trials.  Vitamin D3 form the skin and most supplements as well as D2 from a nutrients is changed into 25OHD by the liver and finally the active 1,25OHD by the kidney.  We use the serum concentration of 25OHD, an expensive test, as indicator of vitamin D status.


We have learned from these studies that levels are lower in the higher latitudes and in winter, because of less sun exposure.  It has been noted that low levels of vitamin D have been linked with many chronic disease states:

• Hypertension
• Stroke
• Congestive heart failure 
• Peripheral arterial disease
• Colon cancer
• Prostate cancer
• Breast cancer
• Diabetes mellitus
• Muscle weakness and falls
• Overall mortality

Studies reveal that women living in areas of little sunlight exposure have more breast cancers and higher mortality rates from the disease.  Several studies, dividing women into groups by 25OHD levels, have shown a decrease in breast cancer risk with higher concentrations of D.  Studies of supplementation have not been consistent.  A Canadian study and a US study have both demonstrated a decrease in breast cancers with supplements of 1000IU and 400IU, but in the Nurses' Health Study, the benefit of supplementation was seen only in premenopausal women.  In the early reports from the Women's Health Initiative there was no benefit seen to supplementation with D3, but in later reports a  decreased breast cancer risk is reported.

Overall, the literature suggests a benefit for reducing breast cancer risk by supplementing Vitamin D, but the trouble with vitamin D is how much.  In these studies, the supplemented amount ranges from 400IU to 4000IU.  Obviously, the total 25OHD is also influenced by diet and sun exposure.  There have also been genetic studies that have shown hereditary variation in D levels in twins living in the same environment.  Four gene polymorphs have been implicated, as well.  

Even experts can't decide what amount to recommend for daily intake.  The Institute of Medicine: 600IU, various Endocrine and Osteoporosis groups: 1000-2000IU and one of the authors in a paper sited above: 4000IU per day.


Excess vitamin D can cause nausea, vomiting, poor appetite, constipation, weight loss, confusion, disorientation, heart dysrhythmias and kidney damage.


The 25OHD concentration is related to intake and there is a toxicity level.  The Food and Nutrition Board (FNB) at the Institute of Medicine studied the problem of daily intake (not the amounts needed to replace a very low level quickly).  Studies have shown that taking 5000IU per day long term leads to a 25OHD concentration of no more than 40-60ng/ml, the toxicity threshold concluded by the FNB review http://www.iom.edu/Activities/Nutrition/SummaryDRIs/DRI-Tables.aspx.  They applied an "uncertainty factor" of 20% and came up with the "tolerable upper intake level" of 4000IU per day.  Again, this is chronic daily long term dose.  More may be required in the short term to increase a severely low level.




You can see that this is difficult issue to study because of all the confounding variables such as inter-individual variation, age, where you live, sun exposure, genetics, ethnicity and even what dose of supplementation.


Clearly, this is a complicated issue and requires personalization for each patient.  On their website The National Cancer Institute concludes that they cannot recommend "for or against" vitamin D supplements for cancer prevention http://www.cancer.gov/cancertopics/factsheet/prevention/vitamin-D.  






The content of this blog is general health information, intended to inform and prompt a conversation with your doctor.  This information is not medical advice.






Together we can prevent 75,000 breast cancer cases each year!