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Calcium Absorption Requires Good Sources of Vitamin D, the Sunshine Vitamin

Good sources of vitamin D are needed in the diet for calcium absorption when sun exposure is limited


I'm pretty sure the world is not coming to an end today, but if the Mayans were right, they were kind enough to plot it on the shortest day of the year.  Short in terms of day light that is. The arrival of the winter solstice means we're not going to be seeing much of the sun for the next few months, so if it isn't doomsday, we need to start looking for other sources of vitamin D.

Did you get your daily dose of the sunshine vitamin today?

What Are the Benefits of Vitamin D?

Even though calcium gets all the credit for keeping our bones strong – in part because it's one of the minerals making up our bones - vitamin D is needed for calcium absorption from the intestinal tract. So no matter how much calcium we ingest, we need vitamin D to get it into circulation so it can eventually reach the bones. Without it, the calcium we consume is excreted in our urine.

In addition to not absorbing calcium when we lack vitamin D, our bones must release calcium into the bloodstream to supply what is needed for other functions in the body when we don't absorb enough. That is why the U.S. started fortifying milk with vitamin D in 1933. The incidence of the crippling bone disease rickets was rising in children following the Industrial Revolution. It was attributed to the fact more people were living and working in cities, so children were getting less exposure to the sun and couldn't make as much vitamin D as they needed. Since calcium is naturally found in milk, vitamin D was added to make sure it was absorbed.

How Does the Sun Help Us Get Our Vitamin D?

When I was in college studying to become a dietitian, I was always on the lookout for a "trick question" about vitamin D on an exam since it's not really a vitamin. Nutritionally speaking, a vitamin is a compound that is essential to life that our bodies cannot manufacture. Vitamin D doesn't fit the bill because we can make what we need if our skin is regularly exposed to ultraviolet light.

The sun was the only source of vitamin D-producing ultraviolet light until the invention of the tanning bed. And though the sun is still capable of supplying all of the bone-building rays we need, many other things have gotten in the way of our benefitting from them. Included on the list are:

  • Widespread use of sunscreens
  • Reduced time spent outdoors
  • Skin covered by clothing
  • Living above or below certain latitudes
  • Living at higher and lower altitudes
  • Lack of exposure to midday sun
  • Thick ozone layers in the atmosphere
  • Heavy cloud cover
  • Skin pigmentation

Other Ways to Get Vitamin D

If you're concerned about calcium absorption, I can't think of a better way to celebrate the winter solstice than with a steaming cup of hot chocolate made with vitamin D fortified milk! You get at least 100 International Units (IU) of vitamin D in every 8 ounce cup of cow's milk whether whole, reduced fat, low fat or fat free. That supplies 25 percent of the Daily Value (DV) of 400 IU for adults and children over the age of 4.  Other dairy products, such as yogurt and cheese, may be fortified and equally good sources. Check the labels on them and all nondairy milk substitutes. Many ready-to-eat breakfast cereals, which partner perfectly with milk, are also fortified with vitamin D, so check the Nutrition Facts on your favorite brands.

Some naturally good sources of vitamin D are:

Foods                                                  IU/serving          % DV

Salmon (sockeye), 3 ounces cooked                         447                   142

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

Sardines, canned in oil, 2 sardines drained              46                      12

Beef liver, 3 ounces cooked                                      42                      11

Egg, large, 1 whole                                                  41                      10

How will you be getting more of the sunshine vitamin this winter?