Vitamin D: It's Not Just Another Vitamin

If I described a substance with the following properties, what would you guess it was?

-It's synthesized by the body from cholesterol
-It crosses cell membranes freely
-It has its own nuclear receptor
-It causes broad changes in gene transcription
-It acts in nearly every tissue
-It's essential for health

There's no way for you to know, because those statements all apply to activated vitamin D, estrogen, testosterone and a number of other hormones. Vitamin D, as opposed to all other vitamins, is a steroid hormone precursor (technically it's a secosteroid but it's close enough for our purposes). The main difference between vitamin D and other steroid hormones is that it requires a photon of UVB light for its synthesis in the skin. If it didn't require UVB, it would be called a hormone rather than a vitamin. Just like estrogen and testosterone, it's involved in many processes, and it's important to have the right amount.

The type of vitamin D that comes from sunlight and the diet is actually not a hormone itself, but a hormone precursor. Vitamin D is converted to 25(OH)D3 in the liver. This is the major storage form of vitamin D, and thus it best reflects vitamin D status. The kidney converts 25(OH)D3 to 1,25(OH)D3 as needed. This is the major hormone form of vitamin D. 1,25(OH)D3 has profound effects on a number of tissues.

Vitamin D was originally identified as necessary for proper mineral absorption and metabolism. Deficiency causes rickets, which results in the demineralization and weakening of bones and teeth. A modest intake of vitamin D is enough to prevent rickets. However, there is a mountain of data accumulating that shows that even a mild form of deficiency is problematic. Low vitamin D levels associate with nearly every common non-communicable disorder, including obesity, diabetes, cardiovascular disease, autoimmune disease, osteoporosis and cancer. Clinical trials using vitamin D supplements have suggested that it may protect against cancer, hypertension, type 1 diabetes, bone fracture and enhance athletic performance. However, the evidence is pretty thin for most of these effects and requires more research.

It all makes sense if you think about how humans evolved: in a tropical environment with bright sun year-round. Even in many Northern climates, a loss of skin pigmentation and plenty of time outdoors allowed year-round vitamin D synthesis for most groups. Vitamin D synthesis becomes impossible during the winter above latitude 40 or so, due to a lack of UVB. Traditional cultures beyond this latitude, such as the Inuit, consumed large amounts of vitamin D from nutrient-rich animal foods like fatty fish.

The body has several mechanisms for regulating the amount of vitamin D produced from sunlight exposure, so overdose from this source appears to be impossible. Sunlight is also the most effective natural way to obtain vitamin D. How much vitamin D is optimal? 30 ng/mL 25(OH)D3 is required to normalize parathyroid hormone levels, and 35 ng/mL is required to optimize calcium absorption.  It's probably best to maintain at least 35 ng/mL 25(OH)D3.

Here's how to become vitamin D deficient: stay inside all day, wear sunscreen anytime you go out, and eat a low-fat diet. Make sure to avoid animal fats in particular. Rickets, once thought of as an antique disease, is making a comeback in developed countries despite fortification of milk (note- it doesn't need to be fortified with fat-soluble vitamins if you don't skim the fat off in the first place!). The resurgence of rickets is not surprising considering our current lifestyle and diet trends. In a recent study, 40% of infants and toddlers in Boston were vitamin D deficient using 30 ng/mL as the cutoff point. 7.5% of the total had rickets and 32.5% showed demineralization of bone tissue! Part of the problem is that mothers' milk is a poor source of vitamin D when the mother herself is deficient. Bring the mothers' vitamin D level up, and breast milk becomes an excellent source.

Here's how to optimize your vitamin D status: get plenty of sunlight without using sunscreen, and eat nutrient-rich animal foods, particularly in the winter. The richest food source of vitamin D is high-vitamin cod liver oil. Blood from pasture-raised pigs or cows slaughtered in summer or fall, and fatty fish such as herring and sardines are also good sources. Vitamin D is one of the few nutrients I can recommend in supplement form. Make sure it's D3 rather than D2; 2,000 IU per day hould be sufficient to maintain blood levels in wintertime unless you are obese (in which case you may need more and should be tested).  Vitamin D3 supplements are typically naturally sourced, coming from sheep lanolin or fish livers. A good regimen would be to supplement every day you get less than 10 minutes of sunlight.

People with dark skin and the elderly make less vitamin D upon sun exposure, so they should plan on getting more sunlight or consuming more vitamin D. Sunscreen essentially eliminates vitamin D synthesis, and glass blocks UVB so indoor sunlight is useless. Vitamin D toxicity from supplements is possible, but exceptionally rare. It only occurs in cases where people have accidentally taken grotesque doses of the vitamin. As Chris Masterjohn has pointed out, vitamin D toxicity is extremely similar to vitamin A deficiency. This is because vitamin A and D work together, and each protects against toxicity from the other. Excess vitamin D depletes vitamin A, thus vitamin D toxicity is probably a relative deficiency of vitamin A.

I know this won't be a problem for you because like all healthy traditional people, you are getting plenty of vitamin A from nutrient-dense animal foods like liver and butter. Vitamin K2 is the third, and most overlooked, leg of the stool. D, A and K2 form a trio that act together to optimize mineral absorption and use, aid in the development of a number of body structures, beneficially alter gene expression, and affect many aspects of health.

Thanks to horizontal.integration for the CC photo.

DART: Many Lessons Learned

The Diet and Reinfarction Trial (DART), published in 1989, is one of the most interesting clinical trials I've had the pleasure to read about recently. It included 2,033 British men who had already suffered from an acute myocardial infarction (MI; heart attack), and tested three different strategies to prevent further MIs. Subjects were divided into six groups:

• One group was instructed to reduce total fat to 30% of calories (from about 35%) and replace saturated fat (SFA) with polyunsaturated fat (PUFA).


• The second group was told to double grain fiber intake.


• The third group was instructed to eat more fatty fish or take fish oil if they didn't like fish.


• The remaining three were control groups that were not advised to change diet; one for each of the first three.
  

Researchers followed the six groups for two years, recording deaths and MIs. The fat group reduced their total fat intake from 35.0 to 32.3% of calories, while doubling the ratio of PUFA to SFA (to 0.78). After two years, there was no change in all-cause or cardiac mortality. This is totally consistent with the numerous other controlled trials that have been done on the subject. Here's the mortality curve:

Here's what the authors have to say about it:

Five randomised trials have been published in which a diet low in fat or with a high P/S [polyunsaturated/saturated fat] ratio was given to subjects who had recovered from MI. All these trials contained less than 500 subjects and none showed any reduction in deaths; indeed, one showed an increase in total mortality in the subjects who took the diet.

So... why do we keep banging our heads against the wall if clinical trials have already shown repeatedly that total fat and saturated fat consumption are irrelevant to heart disease and overall risk of dying? Are we going to keep doing these trials until we get a statistical fluke that confirms our favorite theory? This DART paper was published in 1989, and we have not stopped banging our heads against the wall since. The fact is, there has never been a properly controlled clinical trial that has shown an all-cause mortality benefit for reducing total or saturated fat in the diet (without changing other variables at the same time). More than a dozen have been conducted to date.

On to fish. The fish group tripled their omega-3 intake, going from 0.6 grams per week of EPA to 2.4 g (EPA was their proxy for fish intake). This group saw a significant reduction in MI and all-cause deaths, 9.3% vs 12.8% total deaths over two years (a 27% relative risk reduction). Here's the survival chart:

Balancing omega-6 intake with omega-3 has consistently improved cardiac risk in clinical trials. I've discussed that here.

The thing that makes the DART trial really unique is it's the only controlled trial I'm aware of that examined the effect of grain fiber on mortality (without simultaneously changing other factors). The fiber group doubled their grain fiber intake, going from 9 to 17 grams by eating more whole grains. This group saw a non-significant trend toward increased mortality and MI compared to its control group. Deaths went up from 9.9% to 12.1%, a relative risk increase of 18%. I suspect this result was right on the cusp of statistical significance, judging by the numbers and the look of the survival curve:

You can see that the effect is consistent and increases over time. At this rate, it probably would have been statistically significant at 2.5 years.

I think the problem with whole grains is that the bran and germ contain a disproportionate amount of toxins, such as the mineral-binding phytic acid.  The bran and germ also contain a disproportionate amount of nutrients. To have your cake and eat it too, soak, sprout or ferment grains. This reduces the toxin load but preserves or enhances nutritional value. Wheat may be a problem whether it's treated this way or not.

Subjects in the studies above were eating grain fiber that was not treated properly, and so they were increasing their intake of some pretty nasty toxins while decreasing their nutrient absorption. Healthy non-industrial cultures would never have made this mistake. Grains must be treated with respect, and whole grains in particular.

We're Starting to Get It

I just read an interesting post on the Food is Love blog.

According to the USDA (admittedly not always the most reliable source of accurate information, but we’ll go with it for the moment), the number of farmers markets in the US has risen significantly in the last ten years, from 2,746 in 1998 to 4,685 in 2008. If we get another 580 markets, an increase possible in the next year or two if trends continue, we’ll have tripled the number of recorded markets since 1994.

Furthermore,

Plenty of farmers markets don’t get tallied in official lists, of course. Valereee, over at Cincinnati Locavore, points out that the USDA database only lists a quarter of the markets in her hometown. I see a few missing on the Seattle list as well.

People are slowly starting to get it. We're realizing that the processed food industry does not look out for our best interests. We're realizing that the frailty of modern children as well as our own health problems are due to the outsourcing of agriculture and food preparation. We're realizing that local farms and markets build strong communities.

We're realizing that a return to traditional, wholesome food is the only path to whole health and well-being.


Further reading:
My Real Food manifesto.