Healthy bone is a balancing act. Our bodies continually remove older bone and replace it with new. As adults, if we lose bone at too fast a rate, replace it at too slow a rate, or both, the result is osteoporosis—weak, porous bones that fracture easily. The National Osteoporosis Foundation estimates that nearly 10 million Americans have osteoporosis, and over 43 million more have its precursor—low bone density. The disorder is more common in older than younger people. Fractured bones from this condition can be life-altering, and even life-threatening, but they are not inevitable. There is much we can do to maintain our bones. The earlier we start the better.
What Causes Bone Loss? Bone mass peaks between ages 18 and 25. This peak mass is determined largely by genetics, but nutrition, physical activity, health status during growth, and hormonal and endocrine factors play a role as well. As we age, hormonal changes (particularly menopause); health problems such as thyroid imbalances and digestive disorders; and long-term use of certain medications (including steroids and some heartburn drugs, as well as chemotherapy) all play a role in creating the imbalance that leads to weaker bones. Smoking is associated with lower bone density, as is alcohol abuse. Nutritionally, high salt intake, low calcium intake, and insufficient vitamin D are all associated with higher risk for bone loss, and emerging research suggests other roles for diet as well.
Calcium and Vitamin D: Consuming adequate daily calcium and vitamin D (just as long as you don’t overdo it) is a safe, inexpensive, and evidence-based way to help reduce fracture risk. The bones are the main storage site for calcium, an element which is necessary for many important bodily functions. If we do not get the calcium we need from our diet, the body will take calcium from the bones. Vitamin D plays a major role in calcium absorption. The National Academies of Sciences (NAS) recommends men age 50 to 70 consume 1,000 milligrams (mg) per day of calcium and women age 51 and older and men age 71 and older consume 1,200 mg per day. There is no evidence that intake above these levels provides additional benefits. For vitamin D, the NAS recommends 600 International Units (IU) per day until age 70 and 800 IU per day for those 71 and older, but the National Osteoporosis Foundation recommends an intake of 800 to 1,000 IU per day for adults 50 and older. For both calcium and vitamin D there is evidence that intake above these levels may have adverse effects.
About 75 to 80 percent of the calcium consumed in American diets is from dairy products such as milk, yogurt, and cheese. Calcium is found naturally in plant foods such as dark leafy greens and almonds, and it is sometimes added to processed foods and beverages. Vitamin D is created in the skin upon exposure to the sun’s rays, and is also present to some degree in saltwater fish and liver, and in vitamin D-fortified milk and other fortified foods such as orange juice and cereals.
The use of calcium and vitamin D supplements is controversial. In 2018, the U.S. Preventative Services Task Force concluded that the evidence is insufficient to assess the balance of the benefits and harms of calcium and vitamin D supplementation, alone or combined, for the primary prevention of fractures in most adults, and directly recommended against the use of usual-dose calcium or vitamin D supplements to prevent fractures in community-dwelling, postmenopausal women. Before starting calcium or vitamin D supplements, it is important to discuss the potential benefits and risks with your healthcare provider.
Emerging Ideas: Researchers at Tufts University, led by Bess Dawson-Hughes, MD, director of the Bone Metabolism Laboratory at Tufts’ Human Nutrition Research Center on Aging, are engaged in extensive research on acid-base balance in the body and how it impacts bone health. When food is digested, absorbed, and metabolized, it is broken down into small molecules. Some foods contribute hydrogen ions (H+) which increase the acidity of the blood. “The body needs to keep its acidity level (pH) constant,” says Dawson-Hughes, “and it has a complex system to make that happen.” Bone is a part of that system. “There is a receptor on the bone that triggers an increase in bone breakdown (resorption) when H+ levels in the blood rise,” says Dawson-Hughes. “This process releases alkaline compounds and calcium into the blood. The bone breakdown helps neutralize the acid, but it also weakens bone.”
Research by Dawson-Hughes and colleagues found that adding bicarbonate (an alkali, which neutralizes acid) to the diet reduced markers of bone resorption compared with a placebo. “This experiment leads us to believe that adding foods which are broken down to create alkaline compounds could have a beneficial effect on bone health,” says Dawson-Hughes. Vegetables and fruits (even acidic fruits like citrus) add alkaline compounds to the body. Protein and grains add acidic compounds. “We are not in any way recommending reducing protein intake,” says Dawson-Hughes. “Protein is important to bone and muscle health as we age. It’s the balance that matters. The trick is to reduce grain intake (especially refined grains) and increase fruit and vegetable intake to balance out the grains.” Currently, intake of grains (particularly refined-grains) in the American diet is about twice the recommended amount, and fruit and vegetable intake is below recommendations.
“The bottom line,” says Dawson-Hughes “is that if people adhere to the standard dietary guidelines, they will get the appropriate balance of acid and base, along with plenty of calcium and vitamin D. Our research indicates that the diet that is good for your bones is the same diet that is good for overall health.”