Parwy's Blog: Navigating bone health: early life influences & strategies for improvement & injury prevention

Peter delves into the topic of bone health, explaining why it is an important issue for everyone, from children to the elderly. He begins with an overview of bone mineral density, how it’s measured, how it changes throughout life, and the variability between sexes, largely due to changes in estrogen levels. From there, he provides insights into ways to improve bone health, including exercise, nutrition supplements, and medications.

Mortality Risk and the Importance of Bone Health

Falling, especially leading to a hip fracture, poses an enormous risk of death, particularly for older individuals. The risk of death from a fall by age 75 is substantial.
For people aged 65 or older who fracture their hip in a fall, 25% will be dead in six months.
A hip fracture is a devastating outcome that should be avoided at any age, but especially after the seventh decade and beyond.
A hip fracture carries a greater mortality than smoking. The hazard ratio for all-cause mortality following a hip fracture is 2.78 (a 178% increase in risk of mortality) within one year for participants aged 60 or older, which is higher than the hazard ratio for smoking (which is probably just below 2).
In one study, men aged 90 or above who suffered a hip fracture had a mortality rate of more than 40% within a year. For people over the age of 80, the mortality risk within a year after a hip fracture is about 33%.
Among accidental deaths, for people younger than 60, overdoses are the predominant cause, but for people over 65, falling is the predominant cause.
The most common fractures in people over 65 are in the proximal femur (hip fractures) and the pelvis.

Bone Biology and Definitions

Bone is a living tissue and an organ that is heavily vascularized.
Bone plays a vital role as a reservoir for calcium, as virtually all (around 99%) of the body's calcium is contained within bone. Calcium homeostasis is critical because calcium signaling is important for the activity of every cell.
Bone is constantly being remodeled in an equilibrium. The two key cells involved are:
- Osteoblasts ("B" for building): Responsible for building bone by producing collagen bone matrix and mineralizing it, thus increasing bone mineral density (BMD).
- Osteoclasts: Remove bone by reabsorbing calcified bone and the matrix.
The diagnosis of poor bone health exists on a continuum.
- Osteopenia: Represents about a 10% reduction in bone mineral density relative to a young healthy adult.
- Osteoporosis: Represents about a 25% reduction in BMD relative to a young healthy adult.
The diagnosis of osteopenia and osteoporosis is made by looking at BMD specifically in the hips (left and right) and the lumbar spine (L1 to L5).
There are two types of bone sections: cortical or compact bone (the shaft and exterior of long bones) and trabecular or spongy bone (at the ends of the bone).
Bone marrow is where white cells and red blood cells are produced, and memory B cells and memory T cells that provide lasting immunity against viruses reside in the bone marrow.

Measuring Bone Health with DEXA Scans

The DEXA scan (Dual-Energy X-ray Absorptiometry) is the measurement tool used to determine bone mineral density (BMD). It is a super low-radiation scan.
Not all DEXA scanners are created equal; individuals should confirm that the provider can give segmental bone analysis for the left hip, right hip, and lumbar spine, as many places only offer whole-body BMD.
DEXA results are often reported using:
- T-score: Compares the individual's BMD to that of a young, healthy adult.
- Z-score: Compares the individual's BMD to that of an adult who is their age.
A Z-score of zero means the individual is at the 50th percentile of their age group. A Z-score of +1 means they have a higher bone density than 82.5% of their age population.
Screening recommendations vary widely, but the standard recommendation from many US medical bodies is for women to start screening at 65 and men at 70. However, the WHO is more aggressive, recommending women screen by age 40, and some physicians prefer to screen women in their 30s.

Life Course Changes in BMD and Sex/Race Differences

Bone mineral density (BMD) increases profoundly from about the age of 8 until about 20 years old, with the bulk of BMD accumulation happening during childhood and adolescence. BMD typically peaks in the early 20s and can potentially improve up to age 30.
Men vs. Women: Bone loss affects women much more significantly due to menopause. In the 7 to 10 years around menopause onset, women can lose BMD at a rate of 3 to 7% annually.
In women, BMD is lost primarily in the trabecular or spongy part of the bone (the ends of the bone), whereas the cortical section of bone loss is similar to men.
BMD declines in men over age 65 at a higher rate (typically 1–2% per year) than post-menopausal women, but men start at a much higher point because they avoid the precipitous loss suffered by women post-menopause.
Race Differences: Non-Hispanic black individuals tend to have a higher BMD than non-Hispanic white individuals, who in turn have a higher BMD than Mexican-American individuals.

Estrogen, Hormones, and Bone Remodeling

Bone cells are mechano-sensory cells that sense the load applied by muscles via tendons. When a bone senses a load (stress), it remodels by depositing more bone tissue; bone mass increases in the presence of stress.
This signaling process (the strain signal) is regulated very heavily by estrogen. In the absence of estrogen, this signal is reduced, which is why menopause (sudden estrogen withdrawal) is devastating to bone health for women who do not receive hormone replacement therapy (HRT).
Men also lose estrogen as they age (converted primarily from testosterone), but at a far more gradual rate than women.
Bone mineral density (BMD) health should be a consideration for women thinking about starting HRT. The Women's Health Initiative trial found that HRT decreased fracture risk, which is the single most important metric for benefit.

Essential Nutrition and Supplements

Adequate nourishment is critical for optimizing bone health in children.
The three most important micronutrients for bone deposition are Calcium, Vitamin D3, and Magnesium.
- Calcium: Daily minimum of 1,000 to 1,200 mg. Most of the body's calcium is stored in the bones.
- Vitamin D3/K2: Daily minimum of 800 to 1,000 IU. Vitamin D3/K2 is essential because it increases the gut's absorption of calcium. Deficiency can lead to rickets, a disease resulting in soft, spongy bones.
- Magnesium: Daily minimum of 300 to 500 mg. Many people are likely magnesium deficient through diet alone.
Parathyroid Hormone (PTH) is the master gland for regulating calcium levels. Low calcium stimulates PTH, which in turn stimulates the release of calcium from the bone and converts Vitamin D into its active form to aid in calcium reabsorption from the diet.

The Impact of Physical Activity and Mechanical Loading

Physical activity that loads bones is the most important factor for optimizing bone health, especially during childhood and adolescence.
The greater the force a muscle applies to a bone, the better it is for the bone, as the bone will remodel in proportion to the mechanical stress it is under.
Running may not be enough for optimizing bone mineral density (BMD), potentially because the elite runners studied often have low BMI and may be malnourished for optimizing BMD.
Activities that involve more power, such as jumping and lifting heavy things, are recommended for children.
Resistance training is significantly better at retaining BMD compared to aerobic activities like running, swimming, or cycling, which are considered low-weightbearing activities.
Powerlifting (squat, deadlift, bench press) was found to be more effective than regular strength training in maintaining BMD in post-menopausal women because it heavily stresses the hip and lumbar spine.
High-force impact sports like football and MMA were associated with the highest BMD values.
For adults trying to increase BMD, they must generate "wicked forces on their muscles". Walking with heavy weight (rucking or farmer's carry) and seeking maximum elevation change is a way to apply more strain.
Weight Loss: Losing weight is strongly correlated with a decrease in BMD. This loss can be minimized by combining nutritional manipulation with significant exercise, which may offset hormonal changes and maintain mechanical loading.

Risk Factors and Impairing Drugs

Genetics matter, accounting for up to 50% of bone health. Having a parent with a history of hip fracture is a huge red flag.
Smoking is an independent risk factor for low bone mineral density (BMD). Early smokers (starting before age 16) were found to have the worst bone density later in life compared to late smokers and never smokers.
BMI below 18 or 19 is a risk factor, often related to poor nutritional state and estrogen deficiency, collectively known as the female athlete triad in endurance athletes.
Drugs that impair bone deposition include:
- Corticosteroids: The most important drugs to be cautious about. They impair bone mineralization and inhibit calcium absorption in the gut. Even doses of prednisone as low as 5 mg daily are associated with significant reductions in BMD and increased fracture risk within 3 to 6 months.
- Proton Pump Inhibitors (PPIs): Data is less clear, but observational studies suggest an increased risk of osteoporotic fracture, possibly by interrupting intestinal calcium absorption. However, meta-analyses have not always found a statistically significant decline in BMD with PPI use.
- Anti-epileptic Drugs (e.g., Phenytoin): May lead to increased breakdown of Vitamin D, which in turn decreases calcium absorption in the gut.
Patients taking necessary bone-impairing drugs should be aware of these effects and work harder to counter them.

Immobility, Disuse Osteopenia, and Recovery

Disuse osteopenia occurs when bones are chronically unloaded (e.g., bed rest, paralysis, space travel), leading to an accelerated, unfavorable combination of high bone resorption and low bone formation.
Bone loss due to disuse is incremental and progressive, occurring more rapidly in the trabecular bone. In microgravity or with partial paralysis, this loss can be about 2% per month, and up to 7% per month with complete paralysis.
For individuals experiencing immobility, the focus should be on any form of physical therapy that can actively load muscles. Even isometric movements (resisting against a fixed object) or using techniques like cyclic BFR (Blood Flow Restriction) on unaffected limbs can apply stress to the muscle and potentially reduce bone mineral density (BMD) loss.

Pharmacological Interventions

Drugs are typically the last line of defense for poor bone health.
The main class of drugs is bisphosphonates (e.g., Fosamax, Bonva), which work by slowing the rate at which osteoclasts remove bone.
Studies show that bisphosphonates increase bone mineral density (BMD) by about 4 to 6% in critical areas (hip, lumbar spine) and reduce the risk of fractures. They are typically discontinued after about five years.
Other classes of drugs include monoclonal antibodies and synthetic parathyroid hormone.

Chapters

00:00:00 Intro
00:01:12 Overview of bone health topics to be discussed
00:05:17 Bones 101: bone function, structure, and more
00:08:43 Bone mineral density (BMD), minerals in bone, role of osteoblasts and osteoclasts, and more
00:15:00 The consequences of poor bone health
00:18:55 The devastating nature of hip fractures: morbidity and mortality data
00:25:06 Where fractures tend to occur in the body
00:27:38 Defining osteopenia and osteoporosis
00:30:21 Measuring BMD with DEXA and how to interpret scores
00:38:11 Variability in BMD between sexes
00:41:20 When should people have their first bone mineral density scan?
00:44:32 How BMD changes throughout the life and how it differs between men and women
00:49:27 How changes in estrogen levels (e.g., menopause) impact bone health
00:54:35 Why HRT is not considered a standard of care for postmenopausal bone loss
00:57:48 Factors determining who may be at higher risk of poor bone health
01:02:20 Common drugs that can negatively impact BMD
01:06:26 How children can optimize bone health and lay the foundation for the future
01:12:00 Types of physical activity that can positively impact bone health
01:21:07 How weight loss can negatively impact bone health and how exercise can counteract those effects
01:25:50 Nutrition and supplements for bone health
01:29:16 Pharmaceutical drugs prescribed for those with low BMD
01:34:53 Impact of extreme sedentary periods (e.g., bedrest) and how to minimize their damage to bone