Introduction

Importance of maintaining strong and healthy bones

Ensuring that your bones are strong and healthy is crucial to preserving your overall health and preventing the onset of certain diseases, especially in later life.¹ Bones form the skeleton, a vital organ that not only provides structure, mobility and protection for the body, but also acts as a reservoir for essential nutrients.² 

Overview of sardines as a superfood for bone health

Sardines are a well-known source of omega-3 polyunsaturated fatty acids (n-3 PUFA).¹ This small, oily fish is considered a superfood as it is rich in various nutrients that have many health-promoting benefits. Consumption of sardines can reduce the risk of developing cardiometabolic diseases, including type 2 diabetes mellitus (T2DM), hypertension (high blood pressure) and fatty liver disease. Sardines' nutritious content supports and maintains bone metabolism and cardiovascular health.¹

Incorporating oily fish into your diet is essential for lowering the risk of developing bone-related diseases, such as osteoporosis, which affects 1-in-3 women over the age of 50 and 1-in-5 men worldwide. 

This article will provide an overview of the following key areas:

• The anatomy of bones
• What nutrients are essential for bone health?
• What is the nutritional profile of sardines?
• What health benefits are associated with sardine consumption?
• How to incorporate sardines into your diet
• What are the health concerns associated with sardines?

Bone Health Basics

The anatomy of bones

Structure and function of bones

Bone is a complex living tissue and is primarily composed of calcium (an essential mineral) and collagen (a protein).³ The structural integrity of the skeleton is maintained by minerals bound to proteins, which provide strength, resilience and the ability to withstand impact without shattering.²  

Throughout your growth and development, the skeletal framework changes in size, shape and position through 2 major processes; modelling and remodelling.²  

• Modelling is when a bone is broken down in one place and formed in another, changing its position in the body
• Remodelling involves bone being removed and replaced in the same position 

These processes are controlled by cells that form bone (osteoblasts) and cells that break down bone (osteoclasts). Bones are hollow, enabling your skeleton to be strong and light.² The most numerous cells in bones are called osteocytes, which produce chemical signals in response to mechanical forces that are exerted on the skeleton, during physical activity, for example.² If it is in short supply, calcium stored in the bone can be released into the body to help with vital processes.² 

Bone density and its significance

Bone density is a crucial overall indicator of bone strength and health. A variety of factors can influence bone density, such as genetics, nutrition, hormones and physical activity.⁴ A bone density scan can measure bone weakness and fragility, providing a tool for diagnosing bone-related diseases. Osteoporosis develops over a long period and is characterised by low bone density and a high risk of fracture due to weak bones.⁵ According to the NHS, it affects over 3 million people in the UK and is usually diagnosed in later life when the individual has a sudden fall, causing a fracture.⁵ 

Essential Nutrients for Bone Health

Calcium: The building block of bones

Calcium is a crucial mineral that acts as the primary building block of the human skeleton, providing strength and hardness. Calcium salts are a combination of calcium with other minerals (e.g. calcium phosphate), which help to fill the bone structure (matrix) in a process called bone mineralisation.^6,7 Bones act as a storage site for different nutrients, including calcium, which is the most abundant mineral in your body.⁶ Approximately 99% of your body’s calcium content is contained within bone tissue.¹ Regulating hormones can trigger the release of calcium to support other processes in the body, such as muscle contraction.^2,4 Frequent withdrawals can weaken bones in individuals with a calcium deficiency.² Calcium can be obtained from various dietary sources, including dairy products, fish and leafy green vegetables. 

Vitamin D: Crucial for calcium absorption

Vitamin D is essential for calcium absorption and promotes bone and muscle health.⁶ There are 3 main sources of vitamin D: sunlight, food and dietary supplements.⁸ Exposure to sunlight causes vitamin D synthesis in the skin.⁹ In the Northern Hemisphere, it is recommended to supplement vitamin D from September to April due to low levels of sunlight.⁸ Vitamin D deficiency in adults can lead to osteoporosis or osteomalacia (a painful condition that makes muscle and bone more likely to bend and break).⁶ In children, low vitamin D levels can cause rickets (soft, weak and deformed bones).⁶  Vitamin D is found in eggs, oily fish and some breakfast cereals. However, it is hard to get the recommended amounts from food alone.

Other vital nutrients: Magnesium, phosphorus, omega-3 fatty acids

Additional nutrients such as magnesium, phosphorus and omega-3 fatty acids can contribute significantly to your bone health. Magnesium is essential for the synthesis of vitamin D and improves bone quality.^10,11 In the adult body, 60% of magnesium can be found in bone tissue.¹¹ Like calcium, phosphorus is an essential mineral stored in the bone and can positively influence bone density.^2,11 Phosphorus is vital for other biological processes, such as nerve and muscle function.² Consuming n-3 PUFA offers many nutritional benefits, such as enhancing skeletal health and preventing cardiovascular disease.¹² PUFAs are crucial for cell membrane structure in humans and play a key role in calcium regulation and reducing inflammation.¹² 

The Nutritional Profile of Sardines

Key nutrients in sardines

High in calcium

Sardines are rich in a variety of key minerals, including calcium, potassium, magnesium, zinc and iron.¹ Calcium, a vital multi-functional nutrient, is essential for maintaining bone health throughout your lifespan. A 100g serving of sardines contains 38% of the calcium RDI for adults (382mg).¹   

Rich in vitamin D

Additionally, sardines are an important source of vitamin D, which plays a pivotal role in bone health by increasing calcium absorption. Vitamin D deficiency is a global health issue in both adults and children.¹³ Increasing your sardine consumption could lower the risk of developing bone-related diseases, especially at a mature age. In a 100g serving of sardines, there are 4.8µg of vitamin D.²

Omega-3 fatty acids: Anti-inflammatory effects

Sardines are a cheap, rich dietary source of n-3 PUFAs.¹ PUFAs are vital for vitamin D-dependent calcium absorption, showing the key roles these nutrients play in maintaining bone health.¹² n-3 PUFAs are beneficial for bone health due to their immune-regulating and anti-inflammatory effects.¹² Inflammation significantly contributes to bone-related diseases such as osteoporosis. Higher n-3 PUFA consumption can increase bone density.¹²   

Protein: For bone repair and growth

Dietary protein is vital for bone growth, maintenance and development.¹⁰ Collagen and other proteins form ~50% of your total bone volume.¹⁴ Maintaining a continuous amount of protein consumption in your diet is crucial to support bone metabolism.¹⁰ Studies have shown that a high-protein diet can increase fundamental mediators of bone health, such as insulin-like growth factor-1 (IGF-1).^14,15 Proteins are also associated with higher levels of intestinal calcium absorption and improved muscle strength.^14,15 Sardines are a rich source of proteins that can aid bone repair, containing 24.6g per 100g.¹

Benefits of sardines for bones

Enhancing bone mineral density

High levels of nutrients such as calcium, potassium, iron, phosphorus and magnesium in sardines contribute to improving bone density.¹ Calcium, as an intrinsic part of mineralised connective tissue, provides bone strength and structure.⁴ Magnesium and iron have been shown to positively impact bone density and reduce fracture risk.¹¹ Research has indicated that in postmenopausal women, low dietary intake of magnesium is linked with osteoporosis.¹¹ 

Supporting bone repair and maintenance

Preventing bone loss and fragility relies on healthy eating habits that include vitamins, minerals and other essential nutrients to promote bone health. Osteoporosis is a severe bone-weakening condition that is linked to nutritional deficiencies. Incorporating sardines into your diet can support bone construction by providing protein, calcium, vitamin D and n-3 PUFAs.¹⁰ These nutrients can collectively maintain bone health and enhance fracture healing.¹⁰  

Reducing inflammation and bone loss

Deficiencies in magnesium can promote inflammation and lead to bone loss.¹¹ Research has indicated that inflammation can impact bone remodelling and turnover.¹⁶ Reducing bone loss and inflammation is key to limiting the risk of osteopoenia and osteoporosis. Higher calcium and vitamin D intake has also been linked to reduced bone loss and fracture risk.¹⁰ Eating a healthy, balanced diet that contains sardines can provide n-3 PUFAs, which are known for their anti-inflammatory properties. 

Incorporating Sardines Into Your Diet

How to eat sardines for bone health

Serving suggestions: Fresh, canned, as a snack or in meals

Eating whole sardines is vital to benefit from the high levels of calcium found in the bones. Sardines can be consumed fresh or from a can and added to a quick salad at lunchtime. It is important to note that sardines carrying the blue Marine Stewardship Council (MSC) label are certified as sustainable seafood.¹⁷ Individuals with lactose intolerance can benefit from high calcium in sardines as opposed to consuming dairy products.¹ For instance, 100g of cooked sardines contains the same amount of calcium as ~400ml of milk.¹ Combining easy recipes with sardines is a simple, effective way to improve your bone health. This oily fish can be added to fresh salads, sandwiches or tomato-based pasta dishes to increase their nutritional value and prevent bone loss. 

Making sardines palatable for all ages

Sardines are soft, oily and strong in flavour.¹⁷ They can be made into dips, open sandwiches or fishcakes depending on individual preference. A common way to consume sardines is with lots of lemon juice or on toast with another spreadable condiment. An option that involves avoiding eating whole fish and consuming it as a dip may be more suitable for younger ages, who may find a sardine visually unappealing. Combining it with other flavourful ingredients in a larger cooked meal can help with its incorporation into a balanced diet. These tips can make sardines more appealing and aid individuals in overcoming the strong taste barrier.

Daily intake recommendations for optimal bone health

Ensuring you are consuming the recommended daily intake (RDI) of calcium (700mg per day for adults) is vital to support your bone health. Other RDIs for adults of key nutrients, some of which can be obtained from sardine consumption, are listed below: 

• Vitamin D - 10µg per day
• Phosphorus - 550mg per day
• Magnesium - 300mg per day for men, 270mg per day for women
• Potassium - 3500mg per day

For more information on nutrient intake, please visit the NHS website or seek advice from a healthcare professional. Ensuring that your diet promotes optimal bone health is crucial in preventing cardiovascular or bone-related disease. 

Addressing Health Concerns

Mercury content in sardines: Facts and myths

Mercury is a natural element that, according to the World Health Organisation (WHO), can have toxic effects on the nervous, digestive and immune systems.¹⁸ The organic mercury content (methylmercury) in fish can be traced to its natural occurrence in the Earth’s crust.¹⁸ Mercury is transformed into methylmercury by bacteria.¹⁸ It can then accumulate in fish and become magnified when larger fish eat smaller fish that contain high levels of mercury from digesting plankton.¹⁸ Concern surrounds general fish consumption as high levels of mercury play a role in cardiovascular and neural diseases.¹ However, sardines are near the base of the food web and, as such, are exposed to lower levels of magnesium.¹ Research has shown that increased mercury exposure from regular fish consumption is not associated with a higher risk of cardiovascular disease.¹ Sardines are a safe and wholesome choice for enhancing bone health, making them a beneficial component of a well-rounded and nutritious diet. 

Allergic reactions and how to manage them

Seafood is a popular food item in many countries.¹⁹ However, the consumption of fish or shellfish can lead to serious adverse reactions in susceptible people.¹⁹ Individuals with a seafood allergy can obtain key nutrients to support bone health from alternative food sources such as leafy green vegetables and dairy products. A healthy, balanced diet should include different food groups. If you are concerned about an allergic reaction to sardines due to a pre-existing medical condition, please seek advice from a healthcare professional. 

Summary

The bony skeleton is a crucial organ that must be protected from disease to preserve its structural integrity and capability to act as a storehouse for essential nutrients. Sardines are considered a superfood as they are rich in key health-promoting vitamins and minerals. Consumption of oily fish can reduce the risk of osteopoenia and osteoporosis, which are bone-related diseases associated with the elderly population. Sardines contain high levels of calcium, vitamin D, n-3 PUFA’s and proteins, which are vital for maintaining your overall bone health and metabolism throughout your lifespan. Particular nutrient deficiencies such as magnesium, iron and phosphorus are associated with bone loss and a higher fracture risk. Incorporating sardines into a healthy, balanced diet can offer many beneficial effects, including enhanced bone density, supporting bone repair and maintenance and reducing inflammation. 

Encouragement to explore diverse ways to include sardines in the diet

Although concern surrounds general fish consumption in terms of mercury toxicity in humans, research has shown no increased risk of disease in the consumption of smaller fish, especially those at the bottom of the food chain. Individuals who are allergic to fish should ensure that bone-protective nutrients are gained from alternative food sources to avoid adverse reactions. Sardines are a versatile seafood that can be incorporated into many different palatable meals for easy ingestion across all ages. Raising awareness of the importance of supporting bone density for osteoporosis prevention is critical to encourage further research on the best nutritious foods for bone health. 

FAQs

How do sardines contribute to bone strength?

Sardines are rich in essential nutrients such as calcium, protein, vitamin D and omega-3 fatty acids, which are crucial for maintaining healthy bones. Calcium supports the structure of bones, proteins are vital for bone repair and metabolism, vitamin D enhances calcium absorption and omega-3 fatty acids help reduce inflammation that can lead to bone loss.

Can eating sardines help prevent osteoporosis?

Maintaining bone density is vital to prevent osteoporosis. Consumption of sardines can reduce the risk of osteoporosis by providing high levels of calcium and vitamin D - vital contributors to bone health.

How many sardines should I eat for bone health?

There is no definitive amount of sardines that has been proven to support bone health. However, general recommendations are to consume 2-3 servings a week (about 3.5 ounces per serving) to provide enough calcium and vitamin D to reap the health benefits. 

Are canned sardines as nutritious as fresh sardines for bone health?

Canned sardines retain the nutritional value of fresh sardines. There is no need to be concerned that canned sardines will not support your bone health if included in your diet. It is worth noting that sardines canned in olive oil or water without salt or preservatives are a healthier alternative.

What are the best ways to incorporate sardines into my diet?

Sardines can be eaten in a variety of ways such as in a salad, part of a pasta dish, spread onto a cracker or straight from the can. If you are unsure how to consume them, experiment with different simple recipes to discover the most palatable option. 

Can I rely solely on sardines for my bone health?

Whilst sardines are an excellent source of nutrients for healthy bones, it is important to incorporate them into a healthy, balanced diet that has other sources of calcium, vitamin D and omega-3 fatty acids as well as physical exercise.

Are there any risks associated with eating sardines for bone health?

As with any food item, it is vital to consume sardines in moderation. There is concern surrounding mercury traces in fish consumption, but small fish are generally safe, as they are at the bottom of the food chain. Sardines should be avoided if you have a fish or shellfish allergy. Consult a healthcare professional if you have any concerns.

How does the omega-3 in sardines benefit bone health?

Omega-3 fatty acids in sardines have anti-inflammatory and immune regulatory properties. Inflammation can contribute to bone density loss and has been linked with bone formation and the risk of osteoporosis.