Vitamin D for Osteoporosis
In addition to getting too little calcium, experts cite a silent epidemic of vitamin D deficiency as a contributing factor to osteoporosis. Most foods have little or no natural vitamin D and only a few foods are actually fortified with the vitamin.
Vitamin D acts like a hormone in your body (a hormone is any compound that’s manufactured in one part of the body that affects another part). The active form of vitamin D is made in your liver but it acts on your intestine, your kidneys and your bone. These organs all respond to vitamin D by making calcium available for bone growth. Vitamin D makes calcium and phosphorus available in the blood that bathes the bones, so it can be deposited as bones harden or mineralize. Vitamin D raises blood levels of calcium in three ways—it stimulates your intestine to absorb more dietary calcium, it tells your kidneys to retain calcium and it withdraws calcium from your bones.
As you can see, if you’re lacking vitamin D, you are not getting enough calcium into your body to meet your needs, regardless of how much calcium you consume. A vitamin D deficiency will speed up bone loss and increase the risk of fracture at a younger age.
Vitamin D is different from any other nutrient because your body can synthesize it from sunlight. When ultraviolet light hits your skin, a pre-vitamin D is formed. This compound eventually makes its way to your kidneys, where it’s transformed into active vitamin D.
In the North, the long winter months result in very little vitamin D being synthesized in the skin. Researchers from Tufts University in Boston have demonstrated that blood levels of vitamin D do indeed fluctuate throughout the year.10 They are at their lowest point in February-March and they peak in June-July. But even in the summer, you might not be making enough vitamin D, since the sun protection factor (SPF) in your sunscreen blocks the production of vitamin D. When it is sunny, you should expose your hands, face and arms without sunscreen for 10 to 15 minutes, two or three times a week to help you meet your vitamin D needs.
See the RDA table on page 13 in chapter 1 to see how much vitamin D you should be getting every day. Vitamin D requirements from diet increase with age. This is due to the fact that as we get older, our skin becomes less efficient at producing vitamin D from sunlight.
Unfortunately, good food sources of vitamin D are few and far between. Take a look at the Vitamin D in Foods table on page 14 in chapter 1 to see how the foods you eat make up your vitamin D intake.
Vitamin D Supplements
If you’re over 50, if you don’t drink at least two glasses of a fortified beverage every day or if winter for you means little exposure to sunshine, then you should reach for a good quality multivitamin and mineral supplement. Most products will give you 400 IU of vitamin D. If you take calcium supplements, buy a product with vitamin D added. Fish oil is another way to get your vitamin D, as 1 teaspoon (5 ml) of cod liver oil packs 450 IU. If you take fish oil capsules, make sure you follow the manufacturer’s dosage recommendations or, better yet, get advice from a qualified dietitian or nutritionist. Fish liver oil contains vitamins A and D, two fat-soluble vitamins that are stored in your body. When taken in large doses over a period of time, some types of fish oil supplements can lead to vitamin A and D toxicity.
While calcium and vitamin D are critical to healthy bones, other nutrients are also important players in bone building. Together with calcium and vitamin D, they compose the nutrient team that orchestrates the continual process of bone building and bone breakdown.
One of this vitamin’s important jobs is to support growth and development, especially bone development. I told you earlier that in order to build new bone, the osteoclast cells must first undo parts of old bone. To accomplish this task, osteoclasts contain a sac of degradative enzymes. With the help of vitamin A, these enzymes break down old bone. The fact that bone growth relies on vitamin A is witnessed by the fact that children who are deficient in vitamin A fail to grow properly.
Vitamin A is found pre-formed in animal foods such as fortified milk, cheese, butter, eggs and liver. But we also meet our vitamin A needs by eating bright orange and green fruits and vegetables. The beta-carotene in these plant foods is converted to vitamin A in the body. The best sources of beta-carotene include carrots (surprise!), winter squash, sweet potatoes, spinach, broccoli, rapini, romaine lettuce, apricots, peaches, mango, papaya and cantaloupe.
A number of studies of postmenopausal women have linked higher intakes of vitamin C with having a higher bone density. One study revealed that women aged 55 to 64 years who had taken vitamin C supplements for at least 10 years had significantly higher bone mass compared to women who did not supplement their diet.11 Vitamin C is important for the formation of collagen, a tissue that lends support to bones. This vitamin may also protect bones by acting as an antioxidant and modifying the negative effect of cigarette smoking on bones—many studies have shown that cigarette smoking reduces bone density and increases the risk of fracture.
To get more vitamin C in your diet, reach for citrus fruits, cantaloupe, mango, strawberries, broccoli, brussels sprouts, cauliflower, red pepper and tomato juice. The RDA is 75 milligrams for non-smoking women and 110 milligrams for smokers. To put that in perspective, one medium orange gives you 70 milligrams of vitamin C, and 1/2 cup of red pepper packs 95 milligrams. If you don’t think you consume enough vitamin C in your diet, take a multivitamin and mineral pill each day. Or you might choose a calcium supplement with added vitamin C.
You’ve probably heard very little about this fat-soluble vitamin. One of the reasons for its low profile is that vitamin K deficiency is hardly ever seen. That’s because the millions of bacteria in our intestinal tract synthesize the vitamin. Once we absorb this manufactured vitamin K, it gets stored in the liver. The vitamin is not a part of the bone mineral complex. Instead it helps make a bone protein called osteocalcin. Doctors can measure the amount of osteocalcin in your blood. A high level indicates that your osteoblasts are busy making new bone. Without enough vitamin K, the bones produce an abnormal protein that cannot bind to the minerals that form the bones. The best food sources of vitamin K are leafy green vegetables, cabbage, milk and liver.
When it comes to bone health, the importance of vitamin K should not be underestimated. The famous Nurses’ Health Study from Harvard University found that women with the highest intake of vitamin K had a significantly lower rate of hip fracture compared to women who consumed the least.12 And guess what—eating lettuce was also linked with fewer hip fractures. Lettuce accounted for most of the vitamin K in their diet. Women who ate one or more servings of the leafy green each day (versus one or fewer servings a week) had a 45 percent lower risk of hip fractures.