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MUSCULOSKELETAL HEALTH AND NUTRITION

Nick Krontiris

What are the vitamins and minerals that can help with better musculoskeletal health? What is the current evidence on dietary habits and their impact on musculoskeletal health?

This article aims to examine the micronutrients related to various factors that play a role in musculoskeletal health. These include the importance of calcium, vitamin D, vitamin K and protein.

In addition, we will investigate the role of overall diet quality on musculoskeletal health and the impact of dietary patterns such as the Mediterranean diet.

VITAMIN D, CALCIUM AND VITAMIN K

Vitamin D and calcium work synergistically to promote musculoskeletal health. Vitamin D is essential for intestinal absorption of calcium, as an active metabolite of vitamin D (1,25-dihydroxyvitamin D- 1,25[OH]2D) binds to the vitamin D receptor in the intestinal cell, allowing active calcium transport from the intestine into the circulation.

Dietary vitamin D represents only ∼10-20 % of 25OHD, the major circulating form of vitamin D, whereas the majority (∼80-90 %) is produced through endogenous skin synthesis resulting from direct sun exposure.

Consequently, the amount of dietary vitamin D required may vary based on sun exposure due to geographic location and may also be affected by seasonal changes (summer versus winter) and skin pigmentation.

Suboptimal circulating 25OHD can have an indirect impact on bone by contributing to a reduction in the absorption of ingested calcium, which, in turn, can lead to low calcium levels. This can cause an increase in parathyroid hormone (PTH) secretion, which acts to restore calcium homeostasis through bone resorption. Over time, this can lead to reduced bone density as bone formation is unable to equalize absorption rates, thus increasing the risk of osteoporosis and fractures.

Adequate circulating levels of 25OHD and calcium are not only important for bone health, but also play an important role in muscle physiology and function.

Vitamin D deficiency is associated with disturbances in physiological and neuropsychological function, affecting muscle strength, balance and function, which increase the risk of falls in older people.

Vitamin D supplementation is a common strategy to improve 25OHD status, but the greatest benefits for muscle function appear to be in people with deficiency (25OHD <40 nmol/l), with a lack of benefit in people with adequate 25OHD (≥75 nmol/l).

In short, the benefits of vitamin D are only likely to be seen when there is a deficiency, while dietary supplements are unlikely to lead to further improvements once the Recommended Daily Intake (RDI) of 600-800 IU (15-20 μg) has been achieved and maintained.

Calcium is a major component of bones and teeth and also plays an essential role as a second messenger in cell signalling pathways.

As explained previously, circulating calcium concentrations are tightly controlled by parathyroid hormone (PTH) and vitamin D at the expense of the skeleton when dietary calcium intake is inadequate.

As for the Recommended Daily Intake (RDI) for calcium (1000-1200 mg), this can easily be achieved by consuming a cup of milk (providing ∼276 mg), a cup of yoghurt (providing ∼338 mg) and about half a cup (∼60 g) of cheese (providing ∼438 mg) each day.

Vitamin K exists in two main dietary forms, vitamin K1 (phylloquinones), which is found mainly in vegetables (especially green leafy and cruciferous vegetables, including their oils), and vitamin K2 (menaquinones 4-13), which is found mainly in animal products (e.g. dairy products, cheese, eggs and meat).

The bioavailability of vitamin K1 from cooked vegetables is quite low (up to 10%), which can be slightly increased in the presence of dietary fat.

In contrast, absorption of vitamin K1 from oils is much higher, while long-chain forms of vitamin K2 (menaquinones 7, 8 and 9) have higher bioavailability and absorption rates (close to 100%) from dietary sources such as natto, cheese and egg yolk, with a longer half-life than K1 and menaquinone 4.

Vitamin K plays a vital role in the γ-carboxylation of osteocalcin (OC), a vitamin K-dependent protein (VKDP) associated with bone integrity and produced by osteoblasts.

However, the optimal amount of vitamin K to support musculoskeletal health remains unclear, with current dietary guidelines for vitamin K in various countries typically recommending vitamin K intakes of 90 and 120 μg/day for women and men, respectively.

PROTEIN

Although we have written about protein and musculoskeletal health in previous articles, we will try to be more specific and provide new information in this one.

Several recent systematic reviews and meta-analyses have reported on the association or effects of dietary protein intake on bone density and fracture risk in healthy adults.

These meta-analyses report that higher protein intake is likely to be accompanied by improved bone density for almost all bone areas, from lower risk of hip fracture, or have a neutral effect on the bone density of the lumbar spine, femoral neck and the risk of osteoporotic fracture.

Remarkably, none of these meta-analyses indicated any detrimental effects on bone health, at least in the context of the protein intakes of the included studies.

These positive effects of dietary protein on bone appear to be dependent on the sufficient intake of calcium.

It has been reported that a higher intake of protein and the supplementation of protein can mitigate the age-related decrease in lean mass in middle-aged and older adults.

On the other hand, whether protein intake is positively associated with muscle strength and function is less clear, with evidence to date suggesting that benefits can be observed only when combined with weight training.

It is therefore important to recognise the importance of exercise, especially weight training, for both muscle and bone health.

Regarding the Recommended Daily Intake (RDI) for protein our article provides all the information one could need.

MEDITERRANEAN DIET

To date, compliance to the Mediterranean diet is the eating pattern that has the most consistent correlations with a lower fracture risk.

Indeed, meta-analyses suggest that a higher adherence to the Mediterranean diet is likely to be accompanied by higher bone density at various sites, including the hip, lumbar spine, neck, femur and whole body, as well as with gait speed and lower limb muscle strength, in older adults.

The Mediterranean diet was originally named after studies, publications and books that described the diet of people living in specific areas of the Mediterranean who had a longer life expectancy.

The Mediterranean diet is characterised by a high intake of fibre-rich plant foods such as fruits, vegetables, legumes, cereals and nuts, and a high intake of olive oil and seafood. It also includes moderate consumption of dairy, fish and poultry and lower consumption of red meat, confectionery and processed foods.

Benefits have also been reported among other indicators of dietary quality, such as AHEI and the DASH and lower fracture risk, but with less consistency across studies than for the Mediterranean diet.

From the above, it is evident that a balanced diet rich in fruits, vegetables, unprocessed meat, and fatty fish and dairy products is likely to better meet the overall nutrient requirements for optimizing musculoskeletal health.

Of course, this does not necessarily mean that other types of diets are excluded from being able to provide adequate amounts of the nutrients mentioned above, or that necessarily following such a diet will ensure that one will receive all of them.

In other words, if you have doubts about whether you are getting vitamins D, K, calcium and protein in sufficient amounts for optimal musculoskeletal health, or you want to follow a diet that is not sure to meet these needs, supplements are always a solution.

-Suprastratum: The authority on health, fitness and nutrition

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