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The same thing happens every September
The first cooler weeks arrive, then comes the scratchy throat, followed by a blocked nose – and two weeks later, you are right back where you were this time last year. This is often when people start thinking about immune support, usually once the sore throat has already set in.
But autumn is not difficult because your immune system suddenly stops working properly. What changes is the number of challenges your body has to deal with at the same time. Once you understand what is actually happening in September, you can prepare far more effectively than by reaching for a last-minute course of vitamin C on day three of a cold.
Cold weather does not make you ill: what actually changes in autumn?
Let’s start with one of the most persistent myths. Cold air itself does not cause an infection. You will not catch a cold simply because you went outside with wet hair: colds and flu are caused by viruses, not by low temperatures.
What does change in autumn is our environment – and with it, the conditions in which our immune defenses have to work. We spend more time in enclosed, poorly ventilated spaces, where respiratory infections spread much more easily than they do outdoors. Once the heating comes on, indoor humidity drops, drying out the lining of the nose and throat. This can make the airways less effective at trapping and clearing pathogens because the tiny hair-like structures responsible for moving mucus become less efficient.
Respiratory viruses can also remain infectious for longer in cold, dry air. Schools and nurseries reopen, bringing home a steady supply of seasonal infections for many families. At the same time, changes in the angle of sunlight begin to affect vitamin D production.
Your immune system does not suddenly collapse in September. It simply faces more challenges at once, just as one of its key sources of support – sunlight – starts to disappear.
Five reasons your immune defenses come under more pressure in autumn
- Less sunlight. The skin’s production of vitamin D depends on UVB exposure, which drops sharply as the angle of the sun changes in autumn.
- A change in routine. After the more relaxed pace of summer, earlier mornings, the start of school and a busier workload can all cut into sleep. Lack of sleep has a measurable effect on immune cell activity.
- Ongoing stress. Persistently elevated cortisol can weaken local immune defenses in the mucous membranes, which is one reason why a hectic September can sometimes be followed by illness in October.
- Less movement and fresh air. Regular moderate exercise helps immune cells circulate throughout the body, while spending more time indoors tends to reduce everyday activity.
- Changes in diet. Fresh summer fruit and vegetables are often replaced by heavier, less nutrient-dense foods just as antioxidant intake becomes particularly valuable.
Why do vitamin D3 levels fall in autumn?
Vitamin D3 is not a classic vitamin but a hormone-like substance produced in the skin in response to UVB radiation. At Hungary’s latitude, roughly from October to March, the angle of the sun becomes too low for the skin to produce meaningful amounts of vitamin D.
For around half the year, the body therefore relies largely on the vitamin D stored during the sunnier months and on dietary sources. Because vitamin D is fat-soluble, some can be stored in the body, but these reserves gradually decline over winter. Low vitamin D status is not only relevant to immune function; it may also be associated with fatigue, muscle weakness and generalized aches and pains.
What is happening behind the scenes?
Your immune system works through two closely connected branches. Innate immunity provides the immediate, general response: physical barriers such as the mucous membranes, immune cells that engulf pathogens, and the inflammatory response. Adaptive immunity is slower but more precise, with T and B cells learning to recognize specific pathogens. Cytokines act as messengers between these different parts of the immune system.
Two aspects of this defense depend heavily on adequate nutrient intake. The first is the integrity of the mucous membranes, which form one of the body’s earliest lines of defense. The second is oxidative balance. Immune cells produce free radicals as part of the response to infection, and when antioxidant capacity is insufficient, inflammation can become harder to resolve. This is one reason recovery can feel slow and why symptoms such as coughing may linger even after the fever has gone.
What does “immune boosting” actually mean?
Supporting the immune system does not mean pushing it to work as aggressively as possible. The goal is for it to respond appropriately to a pathogen and then calm the inflammatory response once the threat has passed.
This balanced regulation is known as immunomodulation. Vitamin D plays an important role here: rather than simply “boosting” immunity, it helps regulate how the immune response functions.
How many colds are considered normal?
For adults, around two to four upper respiratory infections a year is considered typical. Young children, especially once they start nursery or school, may experience six to eight. So catching a cold in autumn does not automatically mean there is something wrong with your immune system.
The pattern matters more. It is worth paying attention if infections regularly last longer than three weeks, repeatedly lead to sinusitis or bronchitis, frequently require antibiotics, or if you never seem to recover fully between illnesses.
Cold or autumn allergy?
Some people feel as though they are constantly ill in autumn when the real cause is not an infection at all. Ragweed season peaks in late August, while mould spores from damp leaves and decaying vegetation can remain in the air until the first frosts.
Allergies typically cause itchy eyes and nose, repeated bouts of sneezing and clear, watery nasal discharge. Fever is absent; symptoms can last for weeks, and they are often linked to a particular location or time of day. A cold tends to come on gradually, often beginning with a scratchy throat. Nasal discharge usually becomes thicker after a few days, and symptoms generally resolve within seven to ten days.
If your symptoms appear during the same couple of weeks year after year, it may be worth considering allergy testing.
Natural immune support: what you can do every day
Everyday habits create the foundation for normal immune function. During autumn, it is particularly worth paying attention to the following:
- Aim for seven to nine hours of sleep. Sleep plays an important role in immune memory, and even a single short night can temporarily affect immune defense.
- Air your home several times a day and keep indoor humidity at around 40–60% to prevent the mucous membranes from drying out.
- Exercise regularly, but keep it moderate. A 30-minute walk each day is often more beneficial than one exhausting workout a week.
- Eat enough protein, as immune cells and antibodies are built from amino acids derived from protein.
- Support your gut microbiome with fibre-rich and fermented foods, as a substantial part of the immune system is closely linked to the gut.
- Manage stress deliberately, as chronically elevated cortisol can interfere with local immune defence.
When can targeted nutrient supplementation make sense?
Alongside these lifestyle basics, vitamin D3 deserves particular attention in autumn because natural production drops significantly as sunlight decreases. At the same time, respiratory infections become more common, and the body’s antioxidant defenses may face greater demands. This is why it can make sense to look beyond vitamin D3 alone and consider nutrients that support both normal immune function and protection against oxidative stress.
Why combine vitamins C and D3 with quercetin and grape seed extract?
A daily serving of Riavita Vitamin C + D with Quercetin provides 1,000 mg of vitamin C, 4,000 IU of vitamin D3, 200 mg of Japanese pagoda tree extract standardized to 95% quercetin, and 80 mg of grape seed extract. The formula focuses on two areas that become especially relevant during autumn: normal immune function and antioxidant protection.
Vitamin C contributes to both. It supports the normal function of the immune system and helps protect cells from oxidative stress. That does not mean it prevents colds, but it does provide an essential nutrient the body needs while mounting an immune response.
Vitamin D3 becomes especially relevant because of the timing. Just as the season of respiratory infections begins, natural vitamin D production starts to decline. Supplementation is therefore less about reacting to symptoms once they appear and more about ensuring adequate intake before winter is fully underway.
Quercetin and grape seed extract add plant polyphenols to the formula. They are included for their antioxidant properties, complementing vitamin C by strengthening the antioxidant side of the formulation. Quercetin in particular has attracted considerable research interest as a plant-derived antioxidant.
What does this mean in practice?
The advantage of the combination is that it is not built around a single autumn concern. Vitamin D3 addresses the seasonal decline in vitamin D availability, vitamin C contributes to normal immune function and antioxidant protection, while the plant extracts broaden the formula’s antioxidant profile. Each ingredient therefore has a distinct role rather than simply repeating the same function.
The product may be particularly practical for people who spend their days working around others indoors, live with children who attend school or nursery, or tend to pick up seasonal infections every autumn. It makes most sense to start thinking about support before symptoms appear, when the goal is preparation rather than trying to treat an illness that has already developed.
What should you keep in mind when taking it?
The daily serving contains 4,000 IU of vitamin D3, so it should not automatically be combined with another high-dose vitamin D product. If you already take separate vitamin D or would like a clearer picture of your vitamin D status, a 25-OH-D blood test can help determine whether your current intake is appropriate.
If you are pregnant or breastfeeding, take regular medication, have a history of kidney stones, elevated calcium levels, or thyroid or parathyroid disease, speak to your doctor before using the product.
Timing is one of the most important parts of preparing for autumn. Alongside sleep, regular movement and a varied diet, it makes sense to think ahead about nutrients that are more difficult to obtain in adequate amounts during the darker months. Riavita Vitamin C+D with Quercetin combines vitamin D3, vitamin C and plant-derived antioxidants in a formula designed with this seasonal shift in mind.
