Ode to Vitamin D

It is that time of year again.  School is back in session.  The kids are swapping germs and bringing their new bugs home to their moms and dads who take them to work to swap with their colleagues who then take them home to their kids.  The virus mutates somewhere along the way and the whole cycle starts over. 

 

Ever since I moved north from Texas in 1999, I have managed to contract at least one upper respiratory virus every winter.  It was usually something that robbed me of my voice, had me carrying around a box of Kleenex everywhere I went, left me popping Sudafed and expectorant every 4 hours, and turned me into a cough drop addict.  Most of the time it would take me 3 or 4 weeks to kick these illnesses completely.  Herbal teas and homeopathic remedies provided some relief but nothing terribly lasting.  Extra Vitamin C, echinacea, and zinc kept things from stretching into 5 or 6 weeks.  In the end, I was left to stoically accept that viruses in the Midwest were different than those in Texas and to hope that my immune system would eventually develop a resistance.



Then, in Fall 2009, my cousin mentioned a new study(1) that she had read about Vitamin D deficiency contributing to illnesses, in particular upper respiratory illnesses.  I looked up the study and did some quick research on Vitamin D dosages (and over dosages) and then bought a bottle of Vitamin D supplements.  I started taking an an extra 1000 IUs per day.  For the first time in 10 years the worst I came down with was a case of sniffles and a slight sore throat which lasted all of 24 hours.  I am definitely a believer. 



Now, following my youngest son's nasty and rather frightening, bout with pneumonia last May, I've started my kids on some children's chewable Vitamin D tablets, just an extra 500 IUs per day.  We have managed to get 3 weeks into this school year and the worst they've had so far has been cough and sniffles that lasted about 3 days.  During the past couple of school years, my oldest son has, within the first week of classes, come down with an upper respiratory virus that has last for a minimum of 10 days.  Now I see the other kids in his class coughing and sniffling and I am feeling pretty good that he is not, at least not yet.

What is Vitamin D and from where does it come?

Vitamin D is actually a group of fat-soluble secosteroids.  The two most important of these are Vitamin D2 (aka ergocalciferol) and Vitamin D3 (aka cholecalciferol).(2)  Nutritionally, it is found in relatively small number of foods.  These are fatty fish (e.g. catfish, salmon, mackerel, sardines, tuna, and eel), eggs, beef liver, fish liver oils (e.g., cod liver oil), and mushrooms.   In fact, mushrooms are the only vegan dietary source of Vitamin D.(3)  The label of my Vitamin D supplement does not specify the source but neither does it stipulate that it's source is vegan.  So if you are vegan, I hope you like mushrooms, lots of mushrooms. In some countries, including the USA, some foods such as milk, breakfast cereals, orange juice, flour, margarine, and butter are fortified with Vitamin D.



In vertebrates, Vitamin D is produced in the skin after exposure to ultraviolet-B (UVB) light, either artificial or from the sun.  Peak synthesis occurs when sunlight is at a UV index greater than 3, which occurs daily in the tropics, daily during the spring and summer months  in temperate regions, and almost never in the arctic circles.(4)  Not all outdoor sunlight exposure is equal.  Overcast skies, shade, and air pollution can block UVB rays by as much as 60%.  UVB radiation does not penetrate glass, so sitting indoors in a sunny window does not produce Vitamin D.  Sunscreens with a sun protection factor of 8 or more also block UVB rays, although practically speaking people generally do not apply sufficient amounts or cover all sun-exposed skin, so it is likely that some Vitamin D production will occur anyway.  Clothing also blocks UVB rays.(5) 

Before we all jump the gun and go get a membership at a tanning salon or start visiting the nearest nudist beach, you should consider that some researchers suggest that 30 minutes of sun exposure to the face, arms, legs, or back without sunscreen from late morning to mid-afternoon at least twice a week is enough to provide to sufficient vitamin D synthesis.(6)  Of course this is a generality.  Dark skinned people need longer exposure times than fair skinned people, obese people need more Vitamin D than skinny people,(7) and everyone's body operates uniquely.  Personally, I prefer not to chance the skin cancer.  I use SPF 30+ sunblock, wear hats, and avoid the intense sun during the heat of the day.



How does the body use Vitamin D?

The Vitamin D obtained from sun exposure or diet is biologically inert and must undergo two changes before it is used by the body.  First it is carried in the bloodstream to the liver, where it is converted into a prohormone, calcidiol. The second change takes place in both the kidneys and in the immune system where the circulating calcidiol is converted into calcitriol, the biologically active form of Vitamin D.(8) 



Vitamin D3 aka Cholecalciferol



Vitamin D is essential for to bone strength.  It promotes calcium absorption in the digestive tract and helps maintain adequate serum calcium and phosphate concentrations enabling normal mineralization of bone and preventing hypocalcemic tetany.  It is also needed for bone growth and maintenance.  Without sufficient vitamin D, bones can become thin, brittle, or misshapen, symptoms of rickets, osteomalacia, and osteoporosis.(9)

Vitamin D also plays a significant role in neuromuscular and immune function and reduction of inflammation. It also plays a role in regulating cell proliferation, differentiation, and apoptosis, all of which are important in fighting and preventing cancers.(10)  In the immune system, calcitriol behaves as a cytokine and helps defend the body against microbial invaders.(11)

What are safe doses of Vitamin D?

First know this, I am not a doctor or a pharmacist.  You should talk to yours before you go start or change dosage of any supplements.  This is doubly important if you are on any medication, pregnant, nursing, or undergoing medical treatment for anything.  The only thing I will do is point you to some websites that discuss dosage and talk about why I decided on my own dosage.

 

First, as I mentioned earlier, Vitamin D is a fat soluble vitamin which means that it is stored in the body differently and is easier to over-dose with than a water soluble vitamin, like Vitamin C.  Vitamin D overdose causes hypercalcemia.  Thus, the main symptoms of Vitamin D overdose are those of hypercalcemia.  These include anorexia, nausea, vomiting, polyuria, polydipsia, weakness, nervousness, pruritus, kidney damage, and renal failure.(12) 

A sustained intake of 50,000 IUs can produces toxicity after several months.  However, there can be medical conditions that can make an individuals more sensitive to Vitamin D; thus my cautionary statements.  The U.S. Dietary Reference Intake Tolerable Upper Intake Level (UL or maximum amount that can be tolerated without harm) for infants (birth to 12 months) is 1,000 IUs per day. The UL for children and adults is 2,000 IUs per day.(13)  However, some newer studies indicate that a UL of 10,000 IUs is more appropriate.(14)  These UL numbers are total intake values, dietary, sunlight exposure, and supplemental. 



The Food and Nutrition Board at The National Academies' Institute of Medicine established the Adequate Intake levels (AIs) for Vitamin D based on age alone assuming no exposure to sunlight.  They are 200 IUs for ages birth to 50 years,  400 IUs for 51–70 years, and 600 IUs for 71+ years.(15)  However in 2008, the American Academy of Pediatrics recommended a higher minimum intake of 400 IUs for infants.(16)

In March 2007, a group of vitamin D and nutrition researchers published a controversial and provocative editorial contending that Vitamin D intakes of 400 IUs per day were insufficient to maintain serum Vitamin D levels at optimal levels in healthy adults and that daily intakes of 1,700 IUs should be recommended.(17)  Just as reference, typical diets in the United States provide about 100 IUs per day.(18)

Based on these recommendations and the data presented in the new studies, I have chosen to take an additional 1,000 IUs per day.  This is over and above anything I eat, the 800 IUs in my daily multi-vitamin, and anything I receive via sunlight exposure.  The way I see it, I am most likely getting about 2,000 IUs per day, which is the UL.



With my kids, I am, of course, more cautious.  A smaller intake for smaller people.  I calculate that they are receiving 1,000 IUs per day across diet, multivitamin, Vitamin D supplement, and sun exposure.  This is half the UL for their age group.  Add to that the fact that I cannot always get them to eat the vitamins each day, I am not worried in the least.  I am however, very happy having healthy children when everyone else around them is hacking up a lung. 

I am sure that  we'll all come down with some kind of virus that knocks us on our butts.  It's unavoidable.  However, if the extra Vitamin D makes it easier for our immune systems to handle what we might contract, then it's doing its job.  My goal, to keep my kids and myself out of the hospital due to pneumonia or anything else that tries to take up residence in our chests and have fewer illnesses overall. 

Footnotes

(1) Archives of Internal Medicine. "Association Between Serum 25-Hydroxyvitamin D Level and Upper Respiratory Tract Infection in the Third National Health and Nutrition Examination Survey." Adit A. Ginde, MD, MPH; Jonathan M. Mansbach, MD; Carlos A. Camargo Jr, MD, DrPH. (2009) 169(4):384-390. (http://archinte.ama-assn.org/cgi/content/abstract/169/4/384)

(2) Institute of Medicine.  Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride.  (1997) (http://www.nap.edu/openbook.php?isbn=0309063507&page=250)

(3) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D.  (http://ods.od.nih.gov/factsheets/vitamind.asp)

(4) The American Journal of Clinical Nutrition. "Environmental factors that influence the cutaneous production of vitamin D." MF Holick. (March 1995) 61 (3 Suppl): 638S–645S. (http://www.ajcn.org/cgi/reprint/61/3/638S)

(5) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D.  (http://ods.od.nih.gov/factsheets/vitamind.asp)

(6) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. (http://ods.od.nih.gov/factsheets/vitamind.asp)

(7) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. (http://ods.od.nih.gov/factsheets/vitamind.asp)

(8) Journal of Clinical Endocrinology & Metabolism.  "Update in Vitamin D."  J.S. Adams; M. Hewison (Feb 2010) 95 (2): 471–8. (http://jcem.endojournals.org/cgi/content/abstract/95/2/471)

(9) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. (http://ods.od.nih.gov/factsheets/vitamind.asp)

(10) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. (http://ods.od.nih.gov/factsheets/vitamind.asp)





(11) Journal of Clinical Endocrinology & Metabolism. "Update in Vitamin D." J.S. Adams; M. Hewison (Feb 2010) 95 (2): 471–8. (http://jcem.endojournals.org/cgi/content/abstract/95/2/471)  

(12) Merck Manual of Diagnosis and Therapy, Professional Edition.  "Vitamin D."  Larry E. Johnson, MD, PhD, editor.  (April 2007) (http://www.merck.com/mmpe/sec01/ch004/ch004k.html#sec01-ch004-ch004k-BABBBEAE)
 
(13) Merck Manual of Diagnosis and Therapy, Professional Edition. "Vitamin D." Larry E. Johnson, MD, PhD, editor. (April 2007) (http://www.merck.com/mmpe/sec01/ch004/ch004k.html#sec01-ch004-ch004k-BABBBEAE)
 
(14) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. (http://ods.od.nih.gov/factsheets/vitamind.asp)
 
(15) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. (http://ods.od.nih.gov/factsheets/vitamind.asp)
 
(16) Pediatrics. "Prevention of rickets and vitamin D deficiency in infants, children, and adolescents."  C. L. Wagner; F. R. Greer.  (January 2009) 123(1):197. (http://www.ncbi.nlm.nih.gov/pubmed/18977996?dopt=Abstract)

(17) National Institutes of Health Office of Dietary Supplements. Dietary Supplement Fact Sheet: Vitamin D. (http://ods.od.nih.gov/factsheets/vitamind.asp)

(18) Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride.  (1997) (http://www.nap.edu/openbook.php?isbn=0309063507&page=250)