It is not unusual during a full season of racing to hear about a pro cyclist or two breaking a clavicle or other bone in a multi-rider pile-up. But is there something inherent to cycling that increases your risk for developing a break when you hit the pavement hard? A growing body of research indicates that being fit through cycling training alone does not guarantee optimal bone density. Cycling only may be bad for your bones.

Low bone density is a serious health concern. Osteoporosis is characterized by low bone mass and deterioration of bone tissue over time. This leads to fragile bones and increased risk of fracture of the hip, spine, and wrist. Osteopenia, or sub-normal bone density, precedes osteoporosis. This lower bone mass can increase your risk of getting a fracture. Even if you put in plenty of hard training on the bike, recent studies point to the nature of cycling, such as lack of weight bearing exercise, as being the culprit.

Bone Building tips Add-in weight bearing exercise such as resistance training or running to your training program year round. Aim for at least 1,000 mg calcium daily. Foods and portions providing300 mg daily:

Milk, 8 ounces;

Yogurt, 8 ounces;

Swiss cheese, 1 ounce 200 mg daily:

Cheddar cheese, 1 ounce;

Colby cheese, 1 ounce,

Mozzarella, 1 ounce,

Broccoli, 1 cup cooked;

Collard greens, 1 cup cooked,

Bok choy, 1 cup cooked 100 mg daily:

Cottage cheese, 1 cup;

Dried beans, 1 cup cooked;

Orange, 1 large If you cannot consume 1,000 mg daily from food, consider adding fortified products such as calcium-fortified orange juice. Check labels of products consumed regularly such as recovery drinks and energy bars for calcium content. Add in a calcium supplement of 500 mg daily if your food intake is not adequate or if you need higher amounts of calcium due to existing low bone mass. Increase intake of food sources of vitamin D such as fortified milk and fatty fish. Most cyclists can safely soak up 15 min of direct sunlight three times weekly to produce vitamin D from sunlight, but consider a supplement during the winter months or year round. Aim for 800 IU daily. Cigarette smoking and excess alcohol intake can negatively affect bone mass. Hormone status can affect bone mass. It is established in female athletes that inadequate caloric intake can negatively affect hormone levels, while more data is needed on male athletes.

Earlier research has measured that adult male cyclists have lower bone mineral density than age-matched controls, particularly in masters racers with a long history of exclusive training in cycling; adolescent male cyclists also have lower bone density than expected. Besides the immediate consequence of traumatic bone fractures, cyclists with low bone mineral density put themselves at risk for osteoporosis at a young age. These outcomes and a growing body of evidence should convince male cyclists to pay attention to training and nutrition strategies that maximize bone mass.

The data

One recent study from the University of Oklahoma compared the bone mass of competitive club and professional male road cyclists, most in their late 20’s to early 30’s, to men that matched them in age and body mass and who exercised recreationally. DEXA bone scans indicated the cyclists had lower bone density in the spine compared to controls. About one-fourth of the cyclists had bone density scores classified as osteopenia, while 9 percent had the more severe osteoporosis. Researchers could not relate these results to testosterone levels (a bone regulating hormone in men) or calcium intake, which was actually higher in the cyclists than in the controls, and averaged about 1,500 mg daily, well above recommended guidelines for men. Lower bone density was not seen at the hip site, possibly because cyclists experience greater mechanical loading at the hip than the spine.

Another recent study from the University of Colorado also produced concerning results. Researchers measured bone density in fourteen competitive male cyclists for one year to determine how bone mass may change over the course of a season devoted exclusively to cycling. Similar studies with triathletes and track and flied athletes have generally found no change or positive changes in bone mass in 6 to 12 months of training and competition. Bone mass was found to decrease significantly from the pre-season to off-season in several locations, including the hip, femur, neck, and lumbar spine. Bone mass remained below starting levels in the 3 month off-season period, suggesting that years of competitive cycling can result in progressive bone loss.

Calcium supplements are ineffective

As a sidebar to this study, the cyclists were supplemented with either 1500 mg or 250 mg of calcium citrate daily to augment their daily calcium intake of 700 to 800 mg or so. The 1,500 mg dose was selected to maintain a positive daily calcium balance. While it is above the recommended amounts for men, skin losses of calcium via sweat are estimated at 124 mg/hour of exercise. Potentially, calcium sweat losses over a four-hour ride could exceed 500 mg, contributing to calcium imbalance. However, this supplementation did not affect the rate of bone loss between groups indicating that risk factors other than nutrition played a role. Data on subjects from the study also indicated that blood 25-OH, vitamin D levels were at 30 ng/ml or less, indicating that vitamin D status, a vitamin essential to calcium absorption, may have been less than optimal.

The low impact of cycling exclusively, with no other cross-training can increase your risk for developing low bone density. One study that compared the bone density of cyclists, runners, and weight lifters, found that cyclists had lower bone density than the other two groups. Triathletes have been found to modestly increase bone mass over the season.

It’s all about cross-training.

“Cyclists should be aware that repetitive impact activity is very important for maximizing bone mass,” said Kevin Shea, MD of Intermountain Orthopedic in Boise, Idaho. “They should consider adding weight training and running to their program, and do these activities year round, not just during the off-season.”

Low bone density does increase your risk of getting a fracture, so if you have any concerns about your bone mass, consider getting a bone density scan to establish some baseline data. If you have a slighter build or a family history of low bone density, your risk is increased. Older cyclists may have even lower bone density and a higher risk of fracture even without the trauma of a crash. Female cyclists are at even greater risk of developing low bone density, and bone scans can be important in identifying this early on.

Cyclists heavily focused on their race performance also spend many hours on the bike sweating. Sweat contains a number of minerals other than the more obvious sodium, including calcium. Your calcium sweat losses could add up to several hundred milligrams (mg) over a long ride and increase your calcium requirements. Men are typically advised to obtain 800 mg daily and women about 1,200 mg, though cyclist with low bone mass or at risk could increase their intake calcium intake from food and supplements to 1,500 mg daily. Vitamin D is essential to bone health, and while sunshine is an excellent source, wise use of sunscreen can block vitamin D production and food sources are limited. Many multivitamins contain anywhere from the daily value of 400 International Units (IU) up to the more likely effective and appropriate dose of 800 to 1,000 IU daily. Recommendations for these two important bone building nutrients need to be individualized to each cyclist’s current bone mineral density and risk factors and blood vitamin D status.

Body mass may also play an important role. Many cyclists, despite churning out hundreds or thousands of miles each year, watch their caloric intake closely in hopes of staying light and lean for climbs. Subpar energy intake could have an impact on bone loss in men, just as it can in women, through an impact on the particular sex hormones that affect bone mass in each gender. More research on men is needed, though low testosterone levels have been measured in male endurance athletes.