Vitamin D: A Developing Story

Ten years ago, it is unlikely that vitamin D was on your list of things to worry about.  Now you probably know someone who is vitamin D – deficient and taking a vitamin pill every day – or at least during the winter months when the sun is low in the sky. Finding a magazine or newspaper that hasn’t published stories warning about deficiencies in the “sun vitamin” is difficult. What happened?  Do we have a new problem, or have we just learned more about an old one?

The magic ingredient in cod liver oil

The old part of the Vitamin D story is about a childhood disease called rickets and an adult version of rickets called osteomalacia. Both afflictions became common when urbanization crowded people into the sooty cities of northern Europe in the 1700s. Affected children had bowed legs, malformed chests and teeth, weak muscles and easily fractured bones. In adults, whose bones had stopped growing, the symptoms were bone pain, fractures, and muscle weakness. Though folklore from coastal cities had long described cod liver oil as a remedy for these problems and for other rheumatic complaints, it wasn’t until the early 20th C that scientists discovered that the magic ingredient in cod liver oil was one of the newly described vitamins- special compounds the body can’t make but needs to get in small amounts from specific foods. Vitamin D was the fourth one named, after Vitamins A, B, and C.

Further research demonstrated that Vitamin D is present in many animal fats, and is necessary for the transport of calcium from the intestine into the blood. The rampant rickets and osteomalacia of the early industrial revolution years seemed accounted for by poor diet, but the concentration of these problems in northern climates prompted more questions.  The answers started a new chapter in the story of Vitamin D—its relationship to the sun and its reclassification as a hormone rather than a vitamin.

Vitamin D is actually a hormone, not a vitamin

Vitamin D, as demonstrated by an elegant series of experiments in the 1920s, can be made by the body, in the skin —as long as the skin is exposed to sufficient sunlight. By the time of this discovery though, the vitamin label was too well established to be removed. What started out being known as the bone vitamin became the sunshine vitamin, and more research into its biochemistry placed the “vitamin” firmly in the camp of the  hormones, which are made in the body’s glands and and which act on many different and distant parts of the body to signal changes in cellular functions. Chemically , Vitamin  D most resembles steroid hormones such as testosterone and cortisol and estradiol.

The discovery of Vitamin D receptors

Vitamin D research took its next leap when hormones were discovered to have receptors in the tissues where they were active. Sure enough, Vitamin D had receptors too, in virtually all tissues. By the 1990s researchers were busy trying to find out why. They observed that vitamin D suppressed the growth of cancer cells – at least in the laboratory. Statistical studies showed lower cardiac death rates in the people with the highest vitamin D levels. The bone vitamin suddenly had many possible functions.

In the last decade thousands of studies have attempted to relate hosts of medical problems to vitamin D deficiency, including autism, depression, dementia and other neurodegenerative diseases, many varieties of musculoskeletal pain and arthritis, and autoimmune diseases like multiple sclerosis. So far, most of the research implies that vitamin D exerts its effects in a variety of tissues over the long term, altering the way genes are expressed rather than acting rapidly and directly as it does in intestinal transport of calcium.

Deciding who is deficient in D

Nevertheless, the race is on to see whether or not vitamin D might help many of the ailments that plague us. The first step is trying to decide who is deficient. Measurements of vitamin D, which is a general term applied to a number of different forms of the vitamin, were not standardized until 2006. There is still sometimes contentious debate about which form of the vitamin to measure and what constitutes a normal level.  The general consensus is that vitamin D3 (1-hydroxycholecalciferol) is the best measure of the body’s stores of vitamin D.  The range of normal values of vitamin D3 comes from studies of healthy Hawaiian surfers, who rarely have levels below 30 nanograms (ng)/ml and rarely above 60 ng/ml.  Different laboratories sometimes cite different values, but generally a value in the 20-30 range or lower indicates deficiency.

Requirements change with age

Requirements for vitamin D vary and change over life. As people age, skin produces less. Darker skinned people make less vitamin D. The recommended dose of vitamin D supplements is 200 IU/day (5 micrograms), 400 IU after age fifty, and 600 IU after age 70. Research enthusiasts suggest more.  Sun exposure is by far the most efficient route to adequate vitamin D. Twenty minutes of face and arm exposure produces as much as 10,000 IU vitamin D, which is stored efficiently for weeks. Most supplements are made from the skin of animals or derived from plants chemicals exposed to UV light. (Plant derived vitamin D is known as vitamin D2.)

Rickets makes a comeback

Are we more in need of vitamin D now than previously? In the past, we looked for vitamin D deficiency only in obvious cases of bone disease and kidney failure (the kidney converts vitamin D3 to its most active form). But now, with the best of intentions, we may have created another version of the sunlight deficient, dietary-restricted cities where rickets once thrived. We assiduously shun fat, meat, dairy products and eggs to avoid cardiac disease.  We apply sunscreen liberally to avoid skin cancer. Rickets is on the rise, there are more pediatric bone fractures than in there were a few decades ago, and general arthritic complaints abound. And we now suspect vitamin D may be required for basic cell functions in all organs.

What to do?

A little unprotected sun exposure every few days, and judicious intake of eggs, milk, fatty fish – even a little cod liver oil now and then –  are reasonable tactics to increase the body’s Vitamin D production . Or you could ask your doctor to check a vitamin D blood level and consider taking a supplement if the level is low, especially if you spend the winter above the latitudes of Boston and the California/Oregon border.


                                                    Food Sources of Vitamin D

                                      (From NIH Office of Dietary Supplements)

                                                                                                                                                                                                                                                                                                                                                                       IU         %RDA

Cod liver oil*, 1 tablespoon                                            1,360         340

Salmon (sockeye), cooked, 3 ounces                             794         199

Mackerel, cooked, 3 ounces                                              388           97

Tuna fish, canned in water, drained, 3 ounces            154           39

Milk, vitamin D-fortified, 1 cup                                  115-124    29-31

Yogurt, fortified, 6 ounces                                                  80            20

Margarine, fortified, 1 tablespoon                                    60             15

Sardines, canned in oil, drained, 2 sardines                  46             12

Beef liver, 3.5 ounces                                                             46             12

Fortified ready-to-eat cereal, 0.75-1 cup                        40            10

Egg, 1 whole (vitamin D is in yolk)                                     25              6

*The problem with cod liver oil as a source is that Vitamin A tags along and Vitamin A can be toxic in high doses, producing brain swelling. Check the source information and composition.

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