Hope Santa's got some Cod Liver Oil for us in that sleigh

Monday, December 21st is the Winter Solstice: the shortest day of the year.  What better occasion, then, to issue a wake-up call to my dear readers that you are all most likely deficient (or insufficient) in Vitamin D, the so-called “sunshine vitamin”?  (So much for spreading holiday cheer, huh?)

It’s not your fault, really.  As I’ve written previously, Vitamin D was never supposed to be a dietary vitamin at all.  It’s a hormone that our bodies manufacture from a cholesterol-derived precursor that lives in our skin and gets activated by the sun’s UVB rays.  For millennia of human existence, this system worked pretty well: minimally-clothed people spent long days outside working, hunting and gathering, making loads of D in their skin and storing the excess in their fat cells for the winter months.  Humans who wound up in sunlight-deprived places like Alaska or Scandinavia compensated by evolving into a diet rich in fatty fish–one of the only good naturally-occurring food sources of D, since these fish consume algae that manufacture D from the sun’s UV rays (remember photosynthesis?), and wind up storing it in their fat.  Fast-forward to our modern lifestyles: more time spent indoors, limited outdoor time spent in smoggy cities with tall, sun-blocking buildings, sunscreens, clothing, fortified foods that don’t contain the advertised levels of Vitamin D and a recommended daily value that most experts agree is entirely too low… and lo and behold, we find ourselves in an epidemic of Vitamin D deficiency.

Recent government data from the National Health and Nutrition Examination Survey (NHANES) confirms my own unscientific observations that most of us have insufficient Vitamin D status.  Not a single person I’ve encountered in the past year who had their Vitamin D levels checked–from infants in the hospital I work at to my 30-something year old colleagues to our parents and their 60+ year old friends  — has been Vitamin D sufficient.  The most recent NHANES data I’ve come across, reported in the American Journal of Clinical Nutrition (2008) suggests that about 77% of all American adults are Vitamin D insufficient by currently emerging standards… and an astounding 90% of Mexican Americans and 97% of African Americans are insufficient.  A large study published this past September the journal Pediatrics suggests that prevalence of Vitamin D insufficiency is about 60% in young people aged 1-21.

In other words, unless you are a Caucasian sun-worshipper living in Miami, I’d be willing to bet that you, too, are Vitamin D insufficient.

Why D matters

The association between Vitamin D and rickets– the poor bone mineralization that causes bowed legs and other skeletal deformities in children– is long-established and well-known.  But in the past few decades, evidence has been mounting that points to a crucial role for Vitamin D in a host of other, unrelated health conditions.  Insufficient Vitamin D levels have been associated with an increased prevalence of diabetes, hypertension (high blood pressure) and digestive system cancers (especially esophageal, oral/pharyngeal, colon and pancreatic ).  Poorer vitamin D status has also been associated with higher rates of autoimmune diseases like Type I diabetes, MS, rheumatoid arthritis and Inflammatory Bowel Diseases. (While I haven’t come across any associations specifically to Celiac Disease prevalence and Vitamin D status in the scientific literature, given the autoimmune nature of celiac and its genetic relation to Type I diabetes, its a biologically plausible connection.)  A very recent study published in the Journal of the American Society of Nephrology attributed the increased prevalence of end-stage kidney disease in black men versus white men to the higher prevalence of vitamin D deficiency in black men.

D for Immunity

For immunity, think herring.

I find it curious that so many Americans are obsessed with Vitamin C and its immunity-enhancing benefits.  On average, healthy American adults and children easily meet the daily recommended Vitamin C intake from diet alone (which is 60mg for adults, though smokers will have higher needs of closer to 100mg), and the maximum body pool of vitamin C is associated with daily doses of ~100mg (in adult males).  In other words, given the relatively low turnover of vitamin C in our bodies, daily intake of 100mg/day will saturate your cells and blood with all the vitamin C they can carry (1,500mg total), and all they need to optimize the vitamin C-associated functions they perform, including maximizing your white blood cell response to infectious agents.  Doses beyond 100mg/day are essentially pointless from a nutritional standpoint, and those megadoses of Vitamin C aren’t going to do much beyond filling your pee with vitamin C or give you a mild case of diarrhea.

If you’re serious about optimizing your immune system’s function and are hell-bent on popping a pill to do so, I’d suggest you replace your Vitamin C supplement stash with a Vitamin D one.  Vitamin D is metabolized by our macrophages–the white blood cells that engulf and destroy pathogenic invaders (including cells infected with flu viruses, by the way) that don’t belong there.  Vitamin D induces macrophages to produce one of the proteins responsible for the destruction of these infective agents, so being Vitamin D sufficient is an important condition to supporting the effectiveness of this important immune defense… particularly in sunshine-deprived cold and flu season.  Since most of us do have sufficient Vitamin C levels and don’t have sufficient vitamin D levels, taking a Vitamin D supplement is more likely to enhance our immune system’s strength than taking a Vitamin C supplement.

Get your D

We Vitamin D crusaders are eagerly awaiting a report from the Institute of Medicine in May, 2010 that will contain their committee’s recommendations regarding a possible increase in the current dietary reference intake for Vitamin D– as well as possible increases in the safe upper limit daily dose.  Until that safe upper limit is officially increased, food manufacturers aren’t likely to fortify our milk and cereals with levels high enough to make a difference in our collective Vitamin D status.  Currently, the officially-sanctioned safe upper limit for people over age 1 is 2,000 IU per day. (Your multivitamin or Calcium supplement probably contains somewhere between 100-400 IU/day.)

If you don’t know your Vitamin D status but are concerned about preventing a deficiency, I’d suggest taking 1,000-2,000 IU of supplemental Vitamin D3 per day right off the bat.  (At least in the non-summer months).  If you’re pregnant, I’d suggest starting at 2,000 IU/day, having your Vitamin D levels tested and working with your doctor on a dose that will bring you up to sufficient levels if need be; your needs may turn out to be higher and require a prescription-strength dose to meet them.  If you happen to get tested for Vitamin D and are found to be overtly clinically deficient, your doctor is likely to put you on a prescription-strength repletion protocol to bring your blood levels up to snuff; it usually involves doses from 10,000-50,000 IU for a short period of time, and is then tapered down to maintenance doses of 2,000-6,000 IU/day.

Canned fish, like salmon, mackerel and sardines, are among the best dietary sources of Vitamin D

Of course, maximizing the Vitamin D in your diet will also help.  While surveys have shown that the actual amount of Vitamin D found in fortified dairy is significantly less than what the labels claim (I’ll add this to my list of grievances against the U.S. dairy industry), fortified milk (or your favorite dairy-free milk analogue) is still among the most convenient food sources of Vitamin D. Since Vitamin D is a fat-soluble vitamin–meaning that your intestines absorb it only in the presence of some dietary fat– skim milk isn’t going to do the trick unless you’re having it as part of a meal with some other source of fat.  Go on…switching to 1% milk in your breakfast cereal or latte isn’t going to kill you; for each cup, it’s a 20 calorie difference from skim milk, but those extra 2g of fat will help you absorb the D.  (And ordering your tall, double no-whip latte only ‘half-skinny’ will add another element of snootiness to your custom coffee creation at Starbucks.  Fun!)

Other good food sources of Vitamin D include:

• canned salmon (3oz of canned sockeye salmon contains ~675 IU; your typical farmed salmon fillet will have about half or less due to the lack of algae in the fish’s diet.  Wild sockeye used in canned salmon is among the more sustainable seafood choices available.)
• cod liver oil (1 tsp contains 450 IU.  Grandma knew best!)
• mackerel (3oz of cooked mackerel contains ~390 IU, and Spanish Mackerel is among the more sustainable seafood options currently available)
• herring (3oz of cooked Atlantic herring contains ~180 IU, and is another good choice from a sustainability perspective)
• sardines (3oz of canned sardines contain ~165 IU, and are an excellent choice from a sustainability perspective)
• canned tuna (3oz contains ~150 IU)
• fortified breakfast cereals (check the label, as it will vary by brand, but most contain 10-25% of the current daily value per serving, or about 40-100 IU)
• vitamin D-fortified orange juice (100 IU per 8oz)
• dairy products made with Vitamin D fortified milk (e.g., yogurt.  Typically, one 6oz container contains 80 IU)
• dried shiitake mushrooms (you can, of course, reconstitute them and still get the D.  But its the drying process that activates the D, so fresh shiitakes will not contain the same levels.  My calculations suggest that 1 cup of rehydrated shiitakes (0.5oz, or 3/4 cup, dry) contains about 130 IU of Vitamin D.

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