Seasonal flu not only causes several impacts on health and daily activities but also leaves various potential dangerous complications in adults, especially those with underlying diseases. These following scientific information are shared in this article, which are risks, complications, effective prevention methods (vaccines, hygiene) and the key role of nutrition in enhancing resistance and supporting recovery upon catching seasonal flu.

1.  What is seasonal flu?

Influenza virus is transmitted through the respiratory tract

According to the definition of the World Health Organization (WHO), seasonal flu is an acute respiratory infection caused by influenza virus, circulating globally. Influenza virus has the ability to spread rapidly, causing widespread epidemics every year.

There are three main types of influenza viruses that cause disease in humans: A, B, and C. However, influenza type A and B viruses are responsible for annual seasonal flu epidemics. Influenza type A viruses are classified based on their surface proteins hemagglutinin (H) and neuraminidase (N), such as A(H1N1) and A(H3N2). Influenza type B viruses are divided into two main lineages, B/Yamagata and B/Victoria. Influenza type C viruses usually cause milder disease and do not cause large epidemics ¹.

In Vietnam, seasonal flu may occur year-round but usually peaks in the winter-spring months (usually from October to April of the following year), during the cold and humid weather that is favorable for the development and spread of virus.

2. Understanding seasonal flu and its specific risks in adults

To proactively prevent and effectively respond to seasonal flu, it is important to recognize the typical signs of the disease in adults. At the same time, understanding the causative agent and how the virus spreads allows us to take optimal personal and community preventive measures.

Typical symptoms

Fatigue, runny nose, headache are common symptoms of seasonal flu

Seasonal influenza in adults often begins suddenly with distinct symptoms, including:

•     High fever: Usually above 38°C, lasting several days.
•     Chills: Feeling of shivering accompanied by fever.
•     Headache: Usually severe, concentrated in the forehead and behind the eyes.
•     Body aches: Feeling of muscle and joint pain throughout the body.
•     Fatigue, exhaustion: Feeling of lethargy, severe lack of energy, can last 2-3 weeks.
•     Dry cough: Usually persistent, possibly last after other symptoms have subsided.
•     Other upper respiratory symptoms: May be accompanied by sore throat, runny nose or stuffy nose

Causes and transmission mechanisms

•     Cause: Mainly caused by influenza A and B viruses. An important characteristic of influenza viruses is their ability to continuously change antigens, making it difficult for the immune system of people who have had the disease or been vaccinated before to recognize the new virus strain, leading to annual flu epidemics [1].
•     Transmission route: The influenza virus is transmitted mainly through small droplets containing the virus that are released into the air when an infected person coughs, sneezes or talks. In addition, the virus can also be transmitted through contact with contaminated surfaces (door handles, phones, etc.) and then touching the eyes, nose, or mouth, then entering the body.

3. Serious complications of seasonal flu

Seasonal flu may cause many dangerous health complications

The real danger of seasonal flu often lies in its potential complications. For adults, especially those at high risk such as the elderly (>65 years old) and those with chronic medical conditions, seasonal flu can quickly become a serious health threat.

Pneumonia – The leading and most dangerous complication

Primary influenza pneumonia: Influenza virus directly attacks and severely damages the alveoli in the lungs. This complication often progresses rapidly, causing acute respiratory distress syndrome (ARDS) and has a high mortality rate [2].

Secondary pneumonia due to bacterial superinfection

After the influenza virus damages the respiratory system and weakens the immune system, bacteria such as Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae take the opportunity to invade and cause pneumonia. This is a more common form of pneumonia after the flu, but it is still very dangerous if not treated promptly with appropriate antibiotics ³.

Exacerbation of existing chronic diseases

Influenza virus induces a systemic inflammatory response, placing a heavy burden on the body and possibly triggering exacerbations of many underlying diseases:

–       Respiratory disease: Asthma, chronic obstructive pulmonary disease (COPD) can become worse, leading to severe shortness of breath, respiratory failure.

–       Cardiovascular disease: Flu increases the risk of acute cardiovascular events such as decompensated heart failure, myocardial infarction, stroke.

–       Diabetes: Flu infection causes metabolic disorders, increases blood sugar and makes blood sugar control more difficult in diabetic patients.

–       Chronic liver and kidney disease: Liver and kidney function can be further affected by infection and dehydration.

Other dangerous complications (less common)

In addition to the main complications mentioned above, the influenza virus can also cause other serious damage to the body, although the frequency of occurrence is lower. For example, the virus can directly attack the heart muscle, causing acute myocarditis, affecting the heart’s ability to pump blood. The central nervous system is also not immune, the influenza virus causes encephalitis or meningitis, which can leave long-term neurological sequelae.

Seasonal flu can cause many dangerous complications for the body such as myocarditis, encephalitis or more dangerously, multiple organ failure.

In addition, myositis or even destruction of muscle cells has also been reported, sometimes leading to acute kidney failure. In the most complicated cases, seasonal flu can cause multiple organ failure syndrome, an extremely critical condition that threatens the patient’s life [3].

4. The role of nutrition in preventing and supporting the treatment of seasonal flu in adults

Nutrition plays an important role in preventing and supporting the treatment of seasonal flu in adults

In the “fighting” against seasonal flu, nutrition is not simply food, but the body’s ‘weapon’. Nutrition works on two important fronts: building a strong immune ‘shield’ to prevent illness, and providing ‘fuel’ for strong recovery when the body is infected.

• Nutrition enables seasonal flu prevention: A balanced, nutrient-rich diet to build and maintain a healthy immune system, enhancing the ability to recognize and destroy flu viruses when they invade.
• Nutrition supports treatment and recovery: When sick, proper nutrition provides energy for the body to fight infection, relieve symptoms, compensate for lost fluids and electrolytes, promote recovery, and reduce the risk of complications.

Nutrition to prevent seasonal flu: building an immune “barrier”

To maintain optimal immune system function, it is important to provide adequate amounts of the following nutrient groups:

•     Protein: A component of immune cells and antibodies – important weapons against pathogens. Good sources of protein for the body include: Lean meat (poultry, beef), fish, eggs, milk and dairy products (cheese, yogurt), legumes (soybeans, green beans, lentils), nuts and whole grains.
•     Vitamin C: As a powerful antioxidant, it protects immune cells from damage caused by free radicals generated during the fight against infection. Vitamin C is also necessary for the function of phagocytes and T lymphocytes. Vitamin C is abundant in foods such as: Citrus fruits (oranges, tangerines, grapefruits, lemons), guava, kiwi, strawberries, papaya, bell peppers, broccoli, tomatoes.
•     Vitamin A: Plays an important role in maintaining the integrity of the mucosal barrier of the respiratory and gastrointestinal tracts – the first line of defense against viral invasion. Vitamin A also participates in regulating the function of T and B lymphocytes. Foods rich in Vitamin A include: Animal liver, egg yolks, whole milk, fish oil, carrots, sweet potatoes, pumpkin, spinach, kale, apricots, mangoes.
•     Vitamin E: Also a powerful antioxidant, protecting cell membranes, especially immune cells, from oxidative damage. Foods rich in vitamin E include: Nuts (almonds, sunflowers), vegetable oils (sunflower oil, wheat germ oil), avocados, dark green leafy vegetables.
•     Vitamin D: It is vital in immune regulation, especially in the immune response in the respiratory tract. Vitamin D deficiency is associated with an increased risk of respiratory infections, including influenza. Vitamin D can be supplemented through foods such as salmon, mackerel, herring, egg yolks, mushrooms, and vitamin D-fortified foods (milk, breakfast cereals).
•     Zinc: Essential for the development, differentiation, and function of many immune cells. Zinc deficiency impairs cellular and humoral immune function [4]. Zinc is abundant in foods such as: oysters, clams, red meat, poultry, beans, pumpkin seeds, whole grains, milk.
•     Selenium: As a component of antioxidant enzymes, it protects cells from oxidative stress and participates in regulating inflammatory and immune responses. Dietary sources of Selenium mainly come from seafood (tuna, sardines, shrimp), poultry, eggs and mushrooms.
•     Probiotics and Prebiotics: Probiotics are beneficial bacteria, and prebiotics are food for them. A healthy gut microbiome plays a crucial role in overall immune function through the gut-associated immune system.

○      Sources of Probiotics: Yogurt with live cultures, kefir, sauerkraut, kimchi, tempeh, miso.

○      Sources of Prebiotics: Onions, garlic, leeks, asparagus, bananas, oats, apples, beans.

For the elderly, those at risk of nutritional deficiencies or those who have difficulty eating enough nutrients through regular meals, nutritional supplements such as Nutricare Gold can be a useful support option. Nutricare Gold is researched and developed by the Nutricare Medical Nutrition Institute – USA (NMNI-USA) and Nutricare company, providing a balanced source of nutrition, rich in energy and high-quality protein, easy to digest, allowing to improve health, support musculoskeletal system, cardiovascular system and sleep. Nutricare Gold is supplemented with vitamin complex (A, C, D, E), essential minerals (Zinc, Selenium) and 56 diverse nutrients. Notable among them are vegetable protein and whey protein from the US with vitamin & mineral content that meets the recommendations of the US FDA. Thanks to that, Nutricare Gold helps improve overall health, supports the strengthening of the immune system and improves the body natural resistance, preventing attacks of influenza viruses. In particular, the presence of HMB protects and regenerates muscle mass, prevents common weakness and muscle loss, thereby promoting rapid physical recovery. The product comes in 2 forms: cans and ready-to-drink carton for the convenience of users. It’s recommended to supplement 2-3 glasses per day between main meals to enhance nutrition. Please consult your nutritionist or doctor before use to ensure the best fit for your personal health condition. 

Nutritional support for seasonal flu: reducing symptoms, promoting recovery

When you unfortunately get the flu, your body needs special nutritional support to fight the disease and recover quickly. Specifically with 5 main principles [5] as follows:

•     Provide enough energy: Even if you are tired and have a poor appetite, your body still needs energy to maintain vital functions and the immune system.
•     Easy to digest: Prioritize soft, liquid, easily absorbed foods to reduce the burden on the digestive system.
•     Rehydration and electrolytes: High fever, rapid breathing, and sometimes vomiting can cause dehydration and electrolyte imbalance.
• Supplement with supportive nutrients: Enhancing vitamins and minerals that play a direct role in reducing symptoms and recovery.

Specific nutritional advice

Drink plenty of water: This is a top priority. When you have the flu, you should drink at least 2-2.5 liters of fluid per day (or more if you have a high fever). Good options for rehydration and electrolyte replacement include: Water, unsweetened fresh fruit juice (orange, grapefruit…), warm herbal teas (ginger, mint, chamomile…), broths (chicken/bone broth) or nutritious soups.

Prioritize soft, easy-to-digest foods: Some easy-to-digest dishes, suitable for people with the flu, are: Porridge (chicken, minced meat, fish), Soup (chicken soup, vegetable soup), Stew (bone soup, vegetable soup, etc.). These are all dishes that provide energy and help replenish electrolytes. They are especially easy to digest, enabling quick recovery from the flu.

Increase foods rich in Vitamin C: Some studies suggest that regular doses of 200mg – 1g of Vitamin C per day can shorten the duration of colds and reduce the severity of symptoms when they do occur, especially in children [6]. Therefore, when you have the flu, it is very necessary to supplement foods rich in vitamin C. Some foods rich in vitamin C include: berries such as oranges, tangerines, grapefruit, kiwi, guava, …

People with flu need a balanced and nutritious diet

Supplement foods rich in Zinc: There is evidence that early Zinc supplementation (within 24 hours of symptom onset) may reduce the duration and severity of common cold symptoms [7]. Some foods rich in zinc include oysters, eggs, milk,..

Stay away from irritating foods: To reduce the burden on the digestive system when having the flu, patients should avoid some foods that are difficult to digest, high in fat that can easily cause bloating, discomfort, processed foods, high in sugar, alcoholic beverages such as wine, beer or drinks containing caffeine such as coffee, strong tea because they can easily cause dehydration, inhibit the immune system.

Conclusion

Proper nutrition to prevent seasonal flu effectively

Don’t be subjective, seasonal flu actually has many dangerous complications for adults such as pneumonia or worsening of underlying diseases. Active prevention is the key, with the annual flu vaccine being the core measure, along with personal hygiene and a healthy lifestyle. And to optimize prevention effectiveness as well as support the body when needed, the role of nutrition becomes extremely important. Consider nutrition as an essential foundation for comprehensive health protection during flu season.