This is Part 5 of my Puberty and Growth Series
I started a post on nutrition and puberty but soon realized the information on bone health was just too vast. Clearly, this topic deserves its own post in the series.
In early childhood bone mass builds at a steady rate but that all changes during puberty. In girls, about half of their lifetime total body calcium is deposited during puberty. Boys are even higher — 50-65%.
A 2016 report from The National Osteoporosis Foundation details the lifestyle factors that can help build and sustain bone mass during childhood and beyond. But before we get into that, let’s look at how bone forms throughout the lifecycle
Bone formation and maintenance
Bone is living tissue that grows and expands throughout childhood. This growth is relatively slow until the rapid growth phase of puberty. The peak in bone growth coincides with peak gains in height during puberty — about 12.5 years for girls and 14 years for boys. Ninety-five percent of adult bone mass is reached about four years after this peak.
The active process of bone modeling occurs until peak bone mass is achieved towards the end of the teen years and early twenties. Although bone is always being broken down and replaced, bone repletion dominates this process until about the age of 30. After that, bone mass stops increasing. And after 40 and 50, the breakdown occurs at a faster rate than new bone can be built.
Bone experts explain this process in terms of investing in bone health. When peak bone mass is maximized (lots of deposits!) through lifestyle factors, it decreases the risk of osteoporosis and other problems later in life as demonstrated below.
As children’s bones grow, they first experience an increase in width followed by deposits of calcium. This temporary gap before the achievement of peak bone mass puts children at higher risk for fractures than adults. About half of boys and a third of girls will sustain a fracture by the time they turn 18.
The National Osteoporosis Foundation graded the research linking lifestyle factors to bone health. The only two factors that got an “A” for evidence were physical activity and calcium intake. This means there is solid and consistent evidence that these two factors positively affect bone growth.
Let’s start with calcium. Bone tissue is made up of hydroxyapatite, a calcium-phosphate compound along with magnesium and other trace minerals. Ninety-nine percent of the body’s calcium is stored in bone and withdrawn when more is needed. But over time if there are too many withdrawals and not enough calcium deposits, bone mass and strength can suffer.
At birth, the human skeleton contains only 2-3 percent of total adult body calcium. Recommended intakes of calcium reflect the needs of bone growth during childhood. Below are recommended calcium intakes throughput the lifestyle. Notice recommendations jump up during the peak growth period of puberty. According to The National Osteoporosis Foundation, 0 out of 10 kids in this age range meet the 1300mg (intakes at baseline ranged from 181-1199).
It can feel daunting to meet these needs but don’t get focused on numbers — just increasing calcium sources. Big A does not drink milk or eat cheese (unless on pizza or melted in something). I think it’s important to bring kids into the process and explain the importance of calcium during growth. This way, when they are making their own food choices, they can consider calcium-rich foods. Here’s a link to the 2015 Dietary Guidelines calcium sources and some tips below. I plan to send a printable calcium chart in my next newsletter so if you are interested sign up here. The International Osteoporosis Foundation also has a calcium calculator and downloadable app.
1) Print out calcium sources and explain the why behind increased needs without scaring the child. (Most kids are not concerned with getting osteoporosis down the line but they benefit from understanding they are building strong bones and it helps them no matter what they do).
2) Choose some key calcium sources the children wants to include with meals.
3) Increase calcium in daily meals and snacks including snacks and even dessert. For instance, skip cookies for some nice homemade hot cocoa.
Physical activity also got an “A” for evidence. Research suggests that physically active children have stronger bones than inactive children. Physical activity stimulates bone modeling helping to develop a strong skeleton. Bone responds best to exercises that are non-repetitive, short in duration, and provide a moderate to high “load magnitude.”
Load magnitude (more commonly referred to as weight-bearing exercises) is the level of weight placed on the skeletal system during activity. Examples include impact with the ground (jumping or tumbling), impact with an object (ball or racquet) and the muscle power involved with lifting off the ground like with jumping.
In addition to the recommendation for kids to get 60 minutes or more of physical activity, The National Osteoporosis Foundation recommends bone-strengthening exercise three times a week such as jumping, climbing, and running.
The third most important lifestyle factor for bone health is vitamin D, which got a “B” for evidence.
Vitamin D increases the absorption of calcium from the GI tract and it’s needed for bone growth and modeling. This is why rickets occurs with severe levels of vitamin D deficiency even when calcium intake is adequate.
The RDA for vitamin D for kids age one and older is 600IU. It is difficult to meet recommendations with food sources which include milk, fatty fish, and fortified foods. The sun is also a source but with recommendations for sunscreen, it isn’t a reliable source. Because food sources are lacking most need to supplement — especially in the winter.
Other Dietary and Nutrient Factors
Other nutrients thought to play a role in bone health got a grade “C” or lower meaning the evidence is limited. For example, bone’s connective tissue is made up of protein (collagen). Also, many micronutrients play a key role in connective tissue metabolism including iron, zinc, magnesium, copper, and vitamin K.
Studies show protein can have a positive impact on bone but only when calcium intakes are adequate (>1000mg). High protein diets that are low in calcium may have the opposite effect on bone although more research is needed.
Intake of fiber, fruits, and vegetables seemed to have a positive effect on bone health as well. We will dive into these diet components in a future post.
It’s important to note that other non-controllable factors affect bone health. Genetics account for 60-80% of variation in bone mass and risk for osteoporosis. African Americans have stronger bone density than Caucasians. And among children and adolescents, males have stronger bones mass than females.
But despite these realities, there’s much families can do to invest in bone health during this important time. What concerns you most about your child’s bone health?
Posts Included in the Series:
1. 6 Things About Puberty and Growth Every Parent Should Know
2. The Stages of Puberty: What Families Can Expect
3. How to Get Your Child Through Puberty Without Hating Their Growing Body
4. How to Normalize Sexual Development with Elizabeth Trejos-Castillo [Podcast]