4 nutrients for bone health
Most of us are familiar with the importance of calcium, magnesium, vitamin D, and vitamin K for bone health. And recent research suggests that additional nutrients, including probiotics, may also influence the health of the bones.
But are you confident in your understanding of the different forms of these nutrients, how much of each should be taken at a time, or how they can be combined for the greatest benefit?
Today, we’re going to delve into these questions, using recent research on the five foundational and everyday nutrients for bone health. And we’ll also examine how diet influences bone health from the inside out.
A Refresher on Bone Physiology
Bone is a dynamic tissue that is continuously being broken down and renewed. Bone remodeling involves the coordinated actions of osteoclasts (which are responsible for bone breakdown) and osteoblasts (which are responsible for new bone formation).
Bone remodeling is essential for maintaining the strength, flexibility, and integrity of the bone. However, if there is an imbalance between the activity of osteoclasts and osteoblasts, or if there is a lack of nutrient availability for bone renewal, bone health will decline.
The structural makeup of bone tissue is a good starting point to understand the nutrients required for bone health. Bone tissue consists of approximately 70 percent mineral content and 30 percent organic matter.
The mineral portion of bone is almost entirely (95 percent) calcium hydroxyapatite—a crystalline complex of calcium and phosphorus. The remaining 5 percent consists of other ions, including sodium, magnesium, fluoride, and strontium.
The organic portion of bone is almost entirely (98 percent) collagen fibers, which are supported by a matrix of glycoproteins and proteoglycans.
Top Nutrients for Bone Health
Calcium is the most prominent mineral in the bone, providing strength and density. Calcium also participates in other critical functions in the body, such as muscle contraction, nerve conduction, and intracellular signaling.
Calcium levels are tightly regulated in the blood, and bone serves as a metabolic reservoir—a pool of stored calcium that can be accessed as needed to maintain adequate circulating levels of the mineral throughout the body.
Calcium metabolism is regulated by the interplay of parathyroid hormone (PTH) and calcitonin, but numerous factors—including genetics, hormones, physical activity, and nutrition—influence whether this interplay will result in either the deposition or removal of calcium into bone.
A critical trigger for the removal of calcium from bone (and therefore the decline of bone-mineral density) is inadequate dietary calcium. The recommended total intake of calcium (including diet and supplementation) for adults is 1,000 to 1,200 mg per day.
Milk and other dairy products are rich in calcium, but many plant foods also contain the mineral. Nondairy sources of calcium include vegetables in the Brassica family (e.g., broccoli, kale, cabbage), dark-green leafy vegetables (e.g., collards, dandelion greens, beet greens), canned fish with bones (e.g., sardines), and some nuts and seeds (e.g., almonds and sesame seeds).
Also, calcium in mineral water has been shown to have equivalent bioavailability to calcium in milk, and has been found to support healthy bone-mineral density in randomized, controlled trials.
Despite the many food sources of calcium, many people still don’t consume enough. Therefore, supplementation may be necessary.* But there is great debate over which form of calcium is best for supplementation.
The two most common forms are calcium carbonate and calcium citrate. Calcium carbonate requires stomach acid for absorption, so it’s best taken with meals and is not ideal for people with low stomach acid.
Despite the widely held belief that calcium citrate is more readily absorbed than calcium carbonate, not all studies support this notion. A randomized trial of 24 postmenopausal women found that calcium carbonate and calcium citrate produced equivalent increases in serum calcium over 24 hours.
Some studies suggest that chelated forms of calcium offer superior bioavailability. Calcium lysinate, which consists of calcium chelated with the amino acid lysine, demonstrated superior bioavailability to both calcium carbonate and calcium citrate in a recent clinical trial.
Calcium microcrystalline hydroxyapatite (MCH) is a unique form of calcium extracted from animal bone. A recent randomized trial involving 100 postmenopausal women found that MCH increased blood levels of calcium less than either calcium citrate or calcium carbonate, but had an equivalent effect on bone turnover.
One important thing to consider is that when consuming calcium, the percentage of the mineral that’s absorbed into the body decreases as the intake increases. Because of this, it’s best to spread calcium supplementation throughout the day, and consume no more than 500 mg at a time.
Vitamin D participates in a variety of physiologic functions, including muscle strength, immunity, inflammatory balance, and mood. This vitamin is also essential for bone health because it promotes the absorption of calcium from the gastrointestinal tract.
Studies suggest that vitamin D and calcium confer the most benefit to bones when consumed together. Without adequate vitamin D levels, only 10 to15 percent of dietary calcium is absorbed. But when a person’s vitamin D stores are adequate, calcium absorption increases to 30 to 40 percent.
Many people fail to maintain adequate serum levels of vitamin D. Only small amounts of vitamin D are available from dietary sources, such as fish, or fortified foods. And even though humans synthesize vitamin D from sunlight exposure on the skin, vitamin D deficiency is a still major public health concern worldwide in all age groups, and not readily rectified by dietary changes or even additional sunlight exposure.
Although the current recommended intake of vitamin D is 600 to 800 IUs (15 to 20 mcg) per day for adults, most experts agree that it’s better to focus on achieving optimal serum concentration of 25-hydroxyvitamin D (25[OH]D). While the Endocrine Society says just 30-50 ng/mL guarantees sufficiency, the Vitamin D Council recommends an optimal level of 40-80 ng/mL. Individual production and metabolism of vitamin D varies greatly, meaning some people need to consume more than 1,000 IUs (25 mcg) per day to maintain adequate levels.
Magnesium has an intimate relationship with calcium in the body—in some cases supporting and in other instances antagonizing its effects.
Unlike body calcium, of which 99 percent is stored in the bone, magnesium is more equally distributed between bones, skeletal muscle, and soft tissues. Still, bone is an important reservoir of magnesium, which is incorporated into the hydroxyapatite portion of bone tissue.
But magnesium’s role in bone health doesn’t stop with its structural contribution to bone tissue. Magnesium is necessary for the activity of calcitonin (a hormone that promotes bone formation), for the action of alkaline phosphatase (a critical enzyme for bone formation) and for the metabolism and activation of vitamin D which enhances calcium absorption in the GI tract. Magnesium is required for the binding of vitamin D to its transport protein and the activation of the vitamin in the liver.
Food sources of magnesium include green leafy vegetables, nuts, whole grains, beans, and dark chocolate. But despite the availability of magnesium-rich foods, the U.S. National Health and Nutrition Examination Surveys show that most Americans consume less than the recommended intake of magnesium (310 to 420 mg per day for adults). Consequently, magnesium supplementation may be necessary.*
Also, because of the balancing act between calcium and magnesium, most people who take supplemental calcium should also take supplemental magnesium. The recommended ratio of calcium to magnesium intake is estimated to be 2:1. So if a person is supplementing with 700 mg of calcium per day, he or she would also supplement with 350 mg of magnesium. Best practice of course, is to assess dietary intake of both of these minerals, before deciding on supplementation dosage.
Like calcium, magnesium supplements are available in a variety of forms, and there’s debate as to which form is most effective.
Some studies have found that magnesium aspartate, citrate, lactate, and chloride are absorbed more readily and are more bioavailable than magnesium oxide or magnesium sulfate.
And while chelated minerals are often touted for their superior bioavailability, a small comparison study found that magnesium citrate had better bioavailability than its chelated (magnesium bisglycinate) counterpart. Still, magnesium glycinate is less likely to have bowel effects and may be better tolerated in some individuals than other forms.
Vitamin K is critical for the deposition of calcium into new bone. That’s because the vitamin is a cofactor for a vitamin K-dependent carboxylase, which converts osteocalcin into gamma-carboxylated osteocalcin.
This conversion must take place before osteocalcin can bind to calcium and build bone. Without adequate vitamin K, undercarboxylated osteocalcin accumulates, and calcium can’t be deposited into the hydroxyapatite of bone.
There are two forms of naturally occurring vitamin K. Phylloquinone (vitamin K1) is mostly found in green leafy vegetables. Menaquinones (vitamin K2) are categorized as MK-4 through MK-13, based on their chemical structure.
The best-known menaquinones are MK-4 and MK-7, which are found in animal products (e.g., cheese, meat, egg yolks) and fermented foods (e.g., soy and sauerkraut). MK-7 and almost all other menaquinones can be synthesized by intestinal bacteria. MK-4 is unique, in that it can also be synthesized endogenously—via a process that does not involve intestinal bacteria.
The recommended intake of vitamin K for adults is 90 to 120 mcg per day. However, many studies of vitamin K and bone health have evaluated intakes of 45 mg per day, or 500 times the recommended intake.
None of these studies have reported any serious adverse events. And the Institute of Medicine has established no tolerable upper limit for vitamin K, stating that consumption of the vitamin is “unlikely to cause adverse health effects.”
The best form of supplemental vitamin K is hotly debated. Most experts favor supplementation with vitamin K2, but opinions differ on whether MK-4 or MK-7 is preferable.
Taking 45 mg per day of MK-4 is a standard practice in Japan to support women’s bone health after menopause. Proponents of MK-4 cite studies conducted in Japan and other Asian countries that demonstrate benefits for bone health.
MK-7 is widely available in dietary supplements in the United States—with recommended intakes much lower than 45 mg per day. MK-7 is usually taken between 45 mcg and 90 mcg per day, but studies have evaluated intakes up to 200 mcg per day as safe.
To try and answer the question of whether smaller amounts of MK-4 are beneficial for bones, in 2019, researchers directly compared daily MK-4 intakes of 5 mg and 45 mg. Interestingly, the study showed that 5 mg of MK-4 per day positively affected undercarboxylated osteocalcin levels, while 45 mg offered no additional benefit.
The Role of a Healthy Diet
Nutrient supplementation to support bone health is common, but we can’t dismiss the crucial role of a healthy diet. Genetics and lifestyle interact to determine bone health, but nutrition may be the key factor that determines how genetics ultimately affect bone health.
Whole foods provide an array of micronutrients, phytochemicals, and polyphenols that directly or indirectly influence bone health. Many foods that contain calcium and magnesium, for example, also contain trace amounts of other minerals (such as iron, copper, boron or selenium) that have been found to support the health of bones.
Studies have found that eating prunes for six months supports bone health by providing a good source of vitamin K, manganese, boron, copper, and potassium. Women only need to eat 50 grams (five or six) prunes per day to see benefits.
Other studies repeatedly demonstrate bone-health benefits from eating more fruits and vegetables. One study found that women who ate nine or more servings of specific fruits and vegetables (prunes; citrus fruit; cabbage; garlic; and herbs like parsley, thyme, and rosemary) every day saw benefits for their bones in as little as three months.
There’s no doubt that nutrition influences the health of the bones. Good nutrition begins with a healthy diet, and supplementation can offer additional support. When selecting a supplement to support bone health, keep in mind that multiple vitamins and minerals interact to influence bone metabolism and turnover. Consider supplementation which includes calcium, vitamin D, magnesium, vitamin K, trace minerals and probiotics.