Our human body is guarded from diseases like infections and cancer by the immune system, our natural defense power against disease. If you think of our body as a country, the immune system would be 2 teams of defense – one team would be the military  (or army), and the other team would be the police.

The “Army”

The army and the police work together to maintain the safety of the country (our bodies). The army consists of immune cells we call T cells and B cells, and they make up the majority of about 80% of the immune system. The army normally is on standby mode and does not need to work, unless there is a serious invasion or attack on our body.

The “Police”

However, the police, on the other hand, are always active. They consist of “Natural Killer” cells (or NK cells) and make up 20% of the immune system. The NK cells continuously patrol throughout our whole body and kill virus-infected cells and cancer cells whenever they start to appear, thus effectively stopping them from growing and causing viral infections and cancer in our body.

As you can imagine, our bodies are invaded by viruses each day, as they enter our bodies from the external environment. Even from within our bodies, about 6,000 cancer cells are produced each day during normal body cell growth and replication. If not destroyed, these cancer cells will grow
into tumours.

So, it is of key importance to our health that our immune system functions optimally at all times to minimize the risk of virus infections and cancer occurrence.

How our lifestyle affects the “Police”

According to Dr Ko Okumura of Juntendo University, Japan, “While the power of the ‘army’ of T cells and B cells in our body usually remain constant throughout our lives, the activity level of the ‘police’ or NK cells have been found to be easily reduced by lifestyle factors such as stress, cigarette smoking, lack of exercise and aging. It has also been shown also that low levels of NK cell activity are associated with higher frequency of catching colds, longer time needed to recover from colds and even a higher risk of getting cancer.”

Foods that can help keep the “Police” strong

“Several studies in animals and in also humans have shown that intake of probiotic or ‘good’ bacteria L. casei Shirota (also known as Shirota strain) in the form of cultured milk drinks can help increase NK cell activity. Studies also showed that vitamin C and beta-glucan extracts from shiitake mushroom were able to give similar effects too, but the dose required is much higher than would usually be consumed in the daily diets,” explained Dr Okumura further.

“The immune boosting effects of cultured milk drink can be seen with intake of 40 billion live Shirota strain per day, taken over a three week period. This is equivalent to one to two bottles of probiotics cultured milk per day,” he said.

It is known that lifestyle factors such as stress, smoking and bad eating habits can reduce the activity of the NK cells. Studies conducted by Dr Okumura have shown that drinking cultured milk drink with high probiotic Shirota strain helps to recover NK cells activity that has been reduced, for example in those facing mental stress, heavy smokers and the elderly.

Shirota Strain helps keep the balance

According to Dr Masanobu Nanno, Senior Researcher at the Yakult Central Institute for Microbiological Research, “The Shirota strain has been proven in several clinical studies in humans to help reduce risk of several types of cancers such as colorectal cancer, breast cancer and bladder cancer due to its effect on improving the immune system, in particular the NK cell activity.”

Interestingly, the probiotic Shirota strain not only helps increase NK cell activity that has been reduced, it has also been shown to help reduce allergies, which are actually caused by an overactive immune response. This ‘normalization’ effect on the immune system is currently being further investigated, and we can expect many more such research on the functions of the Shirota strain in various diseases linked to the immune system to be publicized in the near future.

“It is important to note here that the effects of a probiotic on the immune system is specific to particular strains and cannot be generalized to all probiotic strains. The dose required to obtain the effects is also very important,” Dr Nanno elaborates.

A balanced lifestyle helps keep our defenses healthy

On a final note, both Dr Okumura and Dr Nanno emphasized that the best and most important factor for keeping our defenses strong is still maintaining a healthy lifestyle with regular exercise and good eating habits. On top of that, they also recommend consuming a bottle or two of cultured milk containing the Shirota strain daily to keep our “police” defense in tip-top condition, thus keeping diseases at bay.