Many people think of bones as solid forms inside their body that do not change much over time, except maybe during the growing years. Bones are actually quite active throughout a lifetime. They can be both positively and negatively impacted by lifestyle habits. Unfortunately, some of the negative factors can cause bone changes that are not reversible.

Bones are constantly being acted upon by two major types of bones cells osteoclasts and osteoblasts. Osteoclasts dig out old bone tissue similar to pot holes in a road. Osteoblasts act like a road crew that fills in these holes. This leads to ongoing bone turnover.

During childhood and adolescence, the holes being dug are shallower so when they are filled in, it creates a net increase in the bone tissue. This pattern continues until bones reach peak bone mass the most bone that is created for a lifetime in size and density. Females peak at about 19-20 years of age while males have until about 21-22 years of age.

Ideally, during the adult years of young and middle age, the osteoclasts and osteoblasts work at about the same pace which means bone density remains stable, unless there are lifestyle factors that cause a decrease.

Older men progressively begin losing bone at about 1% per year, again unless other factors (like the use of certain medications, undiagnosed celiac disease, malnutrition, etc.) cause more rapid bone loss.

Women undergo a higher percentage of bone loss during the menopausal-postmenopausal period possibly 3% to 5%. After several years, bone loss then slows to an average of about 1% per year, similar to older men. For women, bone loss usually occurs in the spine first since it is more sensitive to changes in estrogen levels. Hip bone density tends to be more related to the aging process.

A number of factors can negatively impact bone over a lifetime. Some of these are modifiable while others are not. Extremely problematic factors include tobacco use, the use of certain medications (such as prednisone), thyroid hormone levels out of the normal range (too high or too low), medical issues or surgeries that reduce nutrient absorption in the intestinal tract, and some cancer treatments.

For women, the length of time that estrogen is actively circulating throughout their lifetime is important. This means that a delay in getting a menstrual period in the adolescent years, not menstruating for extended periods of time in the reproductive years, and early menopause can all lead to reduced bone density. Research suggests that adding an oral contraceptive does not significantly improve bone density in these situations. It appears that natural estrogen cycling is needed.

Women who lose a menstrual period due to insufficient calorie and/or nutrient intake and/or those who consistently do excessive levels of physical activity can increase their risk of bone loss during that time, which is often not recoverable. It can also increase the risk of having a stress fracture, especially in persons doing high impact exercise like running.

Diet plays a key role in bone health. Some nutrients are needed for the structure of bone while others are important for the actual creation of bone. The matrix of bone is made up of protein while the remainder is mostly a wide variety of minerals. Since plants soak up minerals from the soil, they are a great dietary source fruits, vegetables, nuts, seeds, whole grains, and beans and lentils. Dairy products and other dietary calcium sources can provide for the high content of calcium in the bones.

Besides becoming a structural part of bone, some nutrients are involved in the process of creating new bone like vitamin C and B12. Vitamin D is important in regulating the uptake of calcium.

Dietary sources of nutrients are recommended over supplements in most cases (vitamin D is one exception since there are few dietary sources) because foods contain a wider variety of nutrients that work together to keep bones healthy. With dietary sources, there is also not a concern for taking in excessive amounts of individual nutrients that can then lead to potential side effects, imbalances or competition among nutrients for uptake, or toxicity.

Besides the risk of stress fractures, the loss of bone density over time can lead to osteoporosis. Fragile bones have a greater chance of fracture and related consequences. Negative lifestyle habits can mean osteoporosis happens at a younger age than would otherwise occur. For example, a young female who loses her menstrual cycle due to restrictive eating and excessive exercise (and depending on the length of time these factors continue) can end with bone loss that mimics the bone density of an elderly female that may not be recoverable.

The bottom line when it comes to a healthy diet for bones is similar to what is recommended for overall health and reduced risk of many medical problems consuming an appropriate number of calories to achieve and sustain a healthy body weight and eating a wide variety of healthy foods (such as whole grains, fruits, vegetables, lean animal proteins, sufficient amounts of calcium, nuts, seeds, and beans/lentils) to provide needed nutrients.

When it comes to physical activity, both weight-bearing cardiovascular exercise and strength-building exercises can increase bone density in the years before peak bone mass and can help to sustain bone density in all age brackets. Strength exercises are especially important for small-framed, lower weight adults, since these individuals do not benefit as much from weight-bearing exercise. These activities and balance exercises can also reduce the risk of falls and resulting fractures.

Are you taking good care of your bones that will carry you through a lifetime?

Pam Stuppy, MS, RD, CSSD, LD is a registered, licensed dietitian with nutrition counseling offices in York, Maine and Portsmouth, N.H. She has also been the nutritionist for Phillips Exeter Academy, presents workshops nationally, and is Board Certified as a Specialist in Sports Dietetics. (See http://www.pamstuppynutrition.com for more nutrition information, some healthy cooking tips, and recipe ideas).

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HealthBeat: A lifetime of healthy bones - Seacoastonline.com