Does anyone feel confused about nutrition for bone health?
I’ve heard rumors about the dairy industry influencing dietary guidelines. I have travelled to Pacific Islands where dairy foods are hard to come by and osteoporosis wasn’t talked about. I have been told not to worry too much about calcium. I have also been told to eat 3 serves of calcium-rich foods per day. Who do I listen to and what should I believe? I’ve gone on a quest to find out just what we should be focusing on for healthy bones.
It turns out osteoporosis and musculoskeletal conditions are one of the nine Australian National Health Priority Areas. Osteoporosis is a condition where bones become thin, weak and fragile to the point where even a minor bump or accident can cause a fracture or broken bone. In Australia in 2013 there was 1 fracture every 3.6 minutes. By 2022 there will be 1 fracture every 2.9 minutes, errr… that’s crazy?! This is similar to worldwide statistics too, where 8.9 million fractures result from osteoporosis every year. The cost of treating hip fractures and associated morbidity just keeps increasing with our ageing population. You’ve heard this before, but it’s so relevant: PREVENTION IS KEY!
Risk factors of osteoporosis include family history, calcium and vitamin D levels, medical history (including medications), and lifestyle factors such as physical activity, smoking, alcohol intake and body weight. It’s a good idea to check your risk; you’ll find a one minute osteoporosis risk test right here.
Should calcium be the number one focus?
When someone says ‘nutrition’ and ‘bones’ in the same sentence the mind flickers to ‘eat more calcium’, right? Why? It is fact that calcium is the most abundant mineral in the body, and 98% is in the bones and teeth.Tortora GDerrickson B. Principles of anatomy and physiology. 13th ed. Hoboken, NJ: John Wiley & Sons, Inc.; 2012. The other 2% is throughout body fluids, it’s involved in the transmission of messages between nerves, and it helps with maintaining muscle tone and blood clotting.Tortora GDerrickson B. Principles of anatomy and physiology. 13th ed. Hoboken, NJ: John Wiley & Sons, Inc.; 2012. We lose calcium everyday through our sweat, skin, nails, hair, urine and faeces. When the amount of calcium (Ca2+) reduces in the blood, a hormone called parathyroid hormone (PTH) stimulates the bones to release calcium and phosphate. In other words, bones sacrifice their calcium stores to keep blood calcium levels consistent. PTH also enhances the reabsorption of calcium from the kidneys and increases the absorption of calcium from food in the gut via increased production of vitamin D. Fancy stuff, hey! *The body is amazing!*
Given that we are losing calcium all the time, we need to make sure we get enough in the diet to replete our stores. A low bone mineral density is thought to be correlated to higher risk of fracture. Eating more calcium is typically thought to increase bone mineral density, although this concept has recently been challenged in a systematic review of adults over 50 years old. The review found that “increasing calcium intake from dietary sources or by taking calcium supplements produces small non-progressive increases in bone mineral density, which are unlikely to lead to a clinically significant reduction in risk of fracture”. Yep, this supports the concept that our nutrition requirements change as we get older.
How much calcium do we need?
Beverly Merz, from Harvard Medical School says “it’s impossible to determine how much calcium each of us, individually, needs”. This, I agree with. Yet there are evidence-based guidelines that are adequate for ‘most’ people. The Australian Nutrient Reference Values were developed by looking at all available literature and coming up with the best possible recommendations. They say the recommended dietary intake for nearly all healthy adults (females 19-50y, males 19-70y) is 1000mg calcium/day. What does this look like?
1 cup yoghurt (450 mg)
1⁄2 cup bok choy (90 mg)
1⁄2 cup tofu (140 mg)
85g sardines with bones (450 mg)
Total: 1130 mg calcium
Of course, the recommended dietary intake of calcium differs for different population groups; 12-18 year olds, women over 50 and men over 70 are recommended to have 1300mg calcium per day. Meeting calcium recommendations on a vegan diet is challenging, but it can be done! An added challenge is the little chemicals called oxalates in spinach, beetroot greens, and rhubarb. Although these foods have a decent amount of calcium, they are not good sources because their oxalates inhibit the absorption of calcium in the gut.
Can we just take a calcium supplement?
It has been considered safe to take a calcium supplement of 500mg, but taking more than this may increase your risk of heart attack or kidney stones -no thanks! Try to get as much calcium as you can from foods. Another Nutrition Press article discusses calcium supplementation in more depth.
What does vitamin D have to do with bone health?
Vitamin D is involved in the absorption of calcium and phosphorus from the gut. It also works with PTH to maintain calcium homeostasis. Deficiency of vitamin D results in poor use of calcium by the bones and may lead to rickets or osteomalacia (malleable bones). Although vitamin D is essential for body functioning, it’s not an ‘essential nutrient’ because we don’t have to eat it. Our bodies synthesise vitamin D when the skin is exposed to sunlight. The liver and kidneys then help to activate vitamin D. Recommended sun exposure ranges from 5 minutes to 3 hours, depending on skin type, amount of skin exposed, season, time of day and geographic location. Find out how much sun you should be getting here! One more thing: we get a bit of vitamin D from eggs, fortified milk and fish liver oils too!Tortora GDerrickson B. Principles of anatomy and physiology. 13th ed. Hoboken, NJ: John Wiley & Sons, Inc.; 2012.
Why don’t we hear about phosphorus?
After calcium, phosphorus is the next most abundant mineral in the body. Calcium combines with phosphates ‘to form a crystal lattice of mineral salts’ in the bone.Tortora GDerrickson B. Principles of anatomy and physiology. 13th ed. Hoboken, NJ: John Wiley & Sons, Inc.; 2012. Phosphorus is also abundant in the diet; meat, poultry, fish, eggs, dairy, nuts, legumes and whole grains have phosphorous. Think: phospholipid bilayer of cells! Phosphorus deficiency is uncommon, which is probably why we don’t hear about it. But that’s not to say it isn’t important for our skeletal system.
But wait, there’s more
As you’ve probably understood by now, bone health isn’t just about calcium. There’s more than vitamin D and phosphorus too. Our bones use protein, magnesium, antioxidants, phytoestrogens, vitamin C and vitamin K. Like most things in the world of nutrition science, calcium is a single nutrient, and nutrients are only one part of the bigger picture.
Don’t forget physical activity!
A systematic review and meta-analysis found regular physical activity to significantly improve bone strength in children and adolescents by 1-8%, and in premenopausal women by 0.5-2.5%. The study included randomised controlled trials of supervised weight-bearing impact, resistance, or endurance training to assess the whole bone strength, rather than just bone mineral density. The most effective weight-bearing activities include skipping, dancing, jumping and hopping. But these activities can be difficult for older adults, who are currently recommended to perform strength activities 2-3 times a week; e.g. resistance training exercises, lifting and carrying, climbing stairs, moderate yard work or calisthenics (push ups and sit ups). For more information on recommendations for your age group, see the Australian physical activity guidelines.
How to have healthy bones
In short, there are three things to focus on:
- Eat plenty of calcium (and phosphorus) rich foods including dairy, seafood and plant foods
- Get outside to make sure you get enough vitamin D
- Move your body in a way that ‘bears weight’ to strengthen your skeleton
References [ + ]
|1.||⇪abcd||Tortora GDerrickson B. Principles of anatomy and physiology. 13th ed. Hoboken, NJ: John Wiley & Sons, Inc.; 2012.|