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Department of Rheumatology, Allergy and Clinical Immunology and * Department of Nutrition, University of California, Davis, Davis, CA 95616
2To whom correspondence should be addressed.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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(IFN-) production measured. Yogurt consumption,
especially for the live-culture groups, was associated with a
decrease in allergic symptoms in both age groups. Seniors in the
control group experienced an increase in both total and LDL
cholesterol, whereas those in the yogurt groups remained stable during
the course of the study. There was little effect on IFN- and IgE
production, although seniors in the yogurt group had lower levels of
total IgE throughout the year.
KEY WORDS: • immunity • yogurt • immunoglobulin E • interleukin-2 • interleukin-4
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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). The belief that yogurt may be beneficial to
health is centuries old. According to Persian tradition, Abraham owed
his fecundity and longevity to the regular ingestion of yogurt; in the
early 1500s, King Francis I of France was reportedly cured of a
debilitating illness after eating yogurt made from goat's milk
(Deeth and Tamime 1981
). Scientific interest concerning
the health benefits of yogurt was sparked by Metchnikoff in the early
1900s. Metchnikoff proposed that the lactic acid microbes of
fermentation must be antagonistic to the putrefying microbes of the
gut, and, once introduced into the intestine, they would prevent the
breeding of the noxious microbes, which required an alkaline
environment. His hypothesis seemed confirmed by the fact that
populations that regularly ate yogurt lived a very long time (e.g.,
Bulgaria, known for longevity). He experimented on himself and reported
that his health, which was generally poor, improved with regular
ingestion of a sour milk prepared with cultures of the Bulgarian lactic
bacillus. Metchnikoff's enthusiasm about yogurt spilled over into the
public, and doctors began recommending yogurt/sour milk as a hygienic
food. Metchnikoff credited his relatively long life in part to the
lactic bacilli in his diet, and hypothesized, "When people have
learnt how to cultivate a suitable flora in the intestines of children
as soon as they are weaned from the breast, the normal life may extend
to twice my 70 years" (Metchnikoff 1921
).
Recent studies have given support to Metchnikoff's theory that yogurt
may indeed be beneficial to health (Hitchins and McDonough 1989
). Studies show health effects ranging from increased
digestibility of lactose to an increased immune response with the
ingestion of a lactobacillus culture. Yogurt is widely accepted as a
treatment for gastrointestinal distress. It is a good source of calcium
for lactose-intolerant individuals, and has even been reputed to
have hypocholesterolemic effects. Many recent studies have focused on
the possible effect lactobacilli may have on the immune system and the
ability to fight off an infection (Conge et al. 1980
,
DeSimone et al. 1988
, Halpern et al. 1991
, Perdigon et al. 1986 and1987
).
Bloksma et al. (1979)
found that in germ-free
animals ingesting yogurt, there was a nonspecific increase of
immunoglobulin (Ig)3G1, IgG2, IgG2a, IgG2b, and IgM antibodies. Stimulation of lymph
follicles in the spleen of mice fed live cultures also led to an
increase in IgG2a, but repeated experiments did not bear out this
result (Conge et al. 1980
).
It has been found that yogurt potentiates and accelerates the
production and the release of interferon- (IFN-) by cells in
culture, but whether the microorganisms can still potentiate this
effect in vivo remains subject to debate (DeSimone et al. 1986
). DeSimone et al. (1986)
concluded that
yogurt itself was not mitogenic, but that it possessed properties that
potentiated IFN- production. Yogurt's bacteria may potentiate the
production and the release of IFN- by immunocompetent cells and
thereby modulate the host's immune response (DeSimone et al. 1986
). Lactobaccili were found to adhere to lymphocytes in
culture perhaps stimulating the release of IFN-. In an earlier
study, an intriguing increase in the amount of IFN- produced
occurred by stimulated cells from a group eating 450 g of
live-active yogurt daily. Cells of groups consuming heat-killed
yogurt or no yogurt (controls) did not produce a similar increase
(Halpern et al. 1991
).
The few studies to date indicate that lactobacilli activate both a
systemic and a local immune response. Locally, yogurt may enhance the
immune response by increasing the percentage of B lymphocytes and the
phytohemagglutamin (PHA) and lipopolysaccharide (LPS)-induced
proliferative responses of Peyer's patches in the intestine
(DeSimone et al. 1987
). In addition to the potentiating
effects of the organism itself, the peptide products of the
microorganism may possess immunomodulating activity, producing a
systemic effect. Parker et al. (1984)
identified a
hexapeptide that is capable of exerting an anti-infectious
immunostimulatory response on macrophages. Matar et al. (1996)
found that the phagocytic activity of alveolar
macrophages was increased in mice fed fermented milk; when mice were
fed the hexapeptide itself, there was a significant increase in the
resistance to pneumonia infection.
The purpose of this study was to follow the health of a college-aged and senior-aged population during chronic yogurt consumption. Subjects were asked to eat 200 g of plain yogurt every day for 1 y; a group that ate heat-inactivated yogurt and a group that ate no yogurt served as controls. To date, no one has followed the self-reported health of a group eating yogurt for a long period of time. Immune factors in the blood were also followed, and the health questionnaire enabled us to obtain a more complete picture.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Sixty subjects, ranging in age from 20–40 y, and 50–70 y were recruited from the University of California, Davis, student and teaching population. Subjects completed a health questionnaire detailing their health status and the intake of any drugs that would alter the parameters under study. Subjects were accepted into the study if they were free from serious illness for the last 5 y and met the criterion regarding drug intake. Potential subjects were excluded if they had an active infectious disease, autoimmune disease, an active malignancy, documented liver disease, malabsorption syndrome or lactose intolerance. Subjects were not accepted if they were pregnant or nursing.
Protocol.
Subjects were randomly assigned to one of three groups. Group 1 (n = 20) was a control group that refrained from eating yogurt products for the length of the study. Groups 2 (n = 20) and 3 (n = 20) were asked to consume 200 g of yogurt daily for ~1 y. Group 2 was provided with a yogurt in which the culture was heat-killed. Group 3 was provided with a live-active culture yogurt. This was a double-blind study, with neither the researchers nor the subjects knowing which yogurt was live active and which was heat killed. The yogurt, provided by Danon, was 1.5% milkfat, and was similar to commercially available low fat yogurt. Fresh yogurt was delivered every 2 wk. The two yogurts were indistinguishable except that the top of the yogurt cup was either red or blue. Subjects were divided randomly into either the red or the blue group. Health questionnaires were filled out every week for the duration of the study. Additionally, a 4-d food record was collected monthly to monitor dietary practices throughout the study. Records always started on a Wednesday and went through the following Saturday. These records also provided an additional check for compliance with respect to the consumption of yogurt. Blood samples for laboratory analysis were taken at the start of the study and every 3 mo thereafter. Written informed consent was obtained for each subject and the research protocol was approved by the University of California Davis Human Investigation Resource Committee.
Laboratory analysis.
Nonfasting blood samples were obtained by venipuncture from the
antecubital vein. For each blood draw, a complete blood count
(platelets, white and red blood cell counts, hemoglobin and
differential) and a blood chemistry panel [urea nitrogen, creatinine,
urea N/creatinine ratio, Na, K, Cl, CO2, anion gap, Ca,
phosphorous, uric acid, ionized Ca, iron, total protein, albumin,
globulin, albumin/globulin ratios, cholesterol, triglycerides, HDL
cholesterol, LDL cholesterol, alkaline phosphatase,
-glutamyltransferase (GGT) and aspartate aminotransferase (AST)]
were carried out.
Immunologic assays.
Peripheral blood lymphocytes (PBL) were isolated and evaluated for
their ability to generate IFN-. Cells were isolated using
lymphoprep, washed in RPMI, and diluted to 2 x106 cells/mL
in media. The cells were plated onto a 24-well plate and incubated for
72 h with 20 µg/mL of PHA-P. The supernatant
was harvested and measured for IFN-. Radioallergosorbent test (RAST)
analysis of serum IgE was performed for mold, grasses and house dust
mites. In addition, IgE levels were measured by ELISA. During the final
quarter of the study, a subset of the senior subject population
was given a pneumoccocal vaccine. Antibody titers were measured against
four strains (3,6, 10 and 14) of the pneumococcal antigens.
Statistical analysis.
Chemistry panel values, complete blood count values and weights were analyzed by a repeated measures ANOVA. Health questionnaire data were evaluated using a Wilcoxon rank test to compare all time points within a group and a factorial ANOVA for between groups. Differences due to diet treatment were considered significant if the P-value for the effect was <0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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Weekly health questionnaires revealed a significantly lower level of
allergies for the group consuming the live-active yogurt compared
with the heat-killed and no-yogurt groups. Itching was also
significantly lower in the live-active yogurt group. In general,
the group consuming the live-active culture experienced fewer
symptoms overall, as reported in the health questionnaires (Figs. 1
and
2). Although there were no significant differences in any other
self-reported health parameters, there was a trend toward decreased
gastrointestinal distress in the group eating the live-active
yogurt and a trend towards decreased colds, coughing, and wheezing in
the groups consuming yogurt, regardless of culture.
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levels; thus the IFN- levels were
widely variable during this period, with large standard errors. Serum
IgE concentrations for individual allergens were similar among the diet
groups. Total serum IgE for the seniors, however, was significantly
lower at all time points for those subjects consuming yogurt
(Fig. 3
). In the subset of seniors challenged, the response to the
pneumococcal vaccine was similar among diet groups (Table 1).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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).
In an earlier study, our laboratory assessed whether there were any
negative effects associated with the daily consumption of high levels
(450 mg/d) of yogurt. Although the primary focus of the study was to
characterize the effect of yogurt on blood chemistry, descriptive
accounts from subjects in this study concerning their increased
well-being and an intriguing increase in -INF levels led us to
design a long-term study, looking specifically at health
(Halpern et al. 1991
). A level of 200 g of yogurt
was chosen over the previous level of 450 g because this
represents one serving of a dairy product, is easily incorporated into
the daily diet and is a more accurate representation of the average
person's intake.
Similar to our previous study, no adverse effects were associated with
the chronic consumption of yogurt in either age group. What was most
striking was the decreased incidence of allergies in the
live-active yogurt group compared with the other two diet groups in
both the young and senior adults. This study was not begun with
amelioration of allergic symptoms in mind; therefore a population of
mild and non-allergy sufferers were included. Random assignment to
the diet groups led to a wide variance in the levels of IgE and no
differences were noted. However, the senior group not eating yogurt had
consistently higher levels of total IgE. Because they also began the
study with higher levels, it is impossible to draw conclusions from
these data; however, it is worth noting. A future study aimed at atopic
individuals may yield more conclusive results concerning the role of
yogurt in the symptoms of allergy. Work has recently been done by
Wheeler et al. (1997)
in this area. In a
double-blind crossover design, the effect of 450 g/d
live-culture yogurt with or without L. acidophilus was
studied in adult patients with moderate asthma. After two 1-mo
crossover test periods, no significant changes were noted in peripheral
cell counts, IgE, interleukin (IL)-2, or IL-4 when comparing the two
diets. In addition, concanavalin A (Con A)-stimulated lymphocytes from
patients who consumed yogurt containing L. acidophilus
produced borderline elevated IFN- levels (P = 0.054). No differences were noted in mean daily peak flows or changes
in spirometric values, and the quality of life indices were unchanged.
The authors concluded that the live-culture yogurt generated trends
in the increase in IFN- and decreased eosinophilia (Wheeler et al. 1997
). However, these studies were of short duration
compared with others and do reveal the beginning of changes in IFN-
levels similar to those seen in our previous study. In our current
study, the IFN- data were highly variable and thus difficult to
interpret. Baseline levels tended to be very high, obscuring subsequent
measurements. This is in contrast to our previous study in which there
was a clear increase in IFN- seen in the live-culture yogurt
group. One explanation for the lowered IFN- seen is the lower daily
dose of yogurt in the current study. The slight increase seen in the
Wheeler study noted above after only 1 mo of consuming 450 g/d
indicates that a higher daily dose is required to stimulate IFN-
production.
What is responsible for the noted decrease in allergic symptoms is open
to speculation. IFN- may have had an effect by modulating T-cell
function by down-regulating the Th2 response. The fact that
upper respiratory infections, such as colds and flu, were also lower in
the yogurt groups makes this an intriguing possibility. Perhaps
something more specific for modulation of allergic symptoms is
affected. The mechanistic basis for the effect of yogurt on allergies
clearly warrants further investigation.
The senior group experienced a positive response in this study with
respect to cholesterol. The seniors consuming either live-culture
or pasteurized yogurt had the same level of total LDL cholesterol
throughout the study. This is in contrast to the non-yogurt control
group in which both total and LDL cholesterol were increased. As
reported in previous studies, gastrointestinal distress was decreased
in the group eating live-active culture yogurt; although this
decrease was not significant, the trend supports data reported in
previous studies (DeDios Pozo-Olano et al. 1978
,
Tanaka 1982
).
The studies reported here, together with studies by several other investigators, indicate that there is a role for fermented milk products in the modulation of the immune system. Live-culture yogurt presents a good immune stimulatory/modulatory food that can be comfortably added to the average daily diet and is easily assimilated by most individuals. In-depth studies of the mechanisms behind stimulation of the immune system by Lactobacillus would provide valuable information regarding the role of microorgansims in intestinal immunity.
Abbreviations used: AST, aspartate aminotransferase; Con A,
concanavalin A; GGT, -glutamyltransferase; IFN-, interferon-;
Ig, immunoglobulin; IL, interleukin; LPS, lipopolysaccharide; PBL,
peripheral blood lymphocytes; PHA, phytohemagglutamin; RAST,
radioallergosorbent test.
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FOOTNOTES |
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1 Presented at the conference Nutritional and
Health Benefits of Inulin and Oligofructose held May 18–19, 1998 in
Bethesda, MD. This symposium was supported in part by educational
grants from the National Institutes of Health Office of Dietary
Supplements, the U.S. Department of Agriculture and Orafti Technical
Service. Published as a supplement to The Journal of
Nutrition. Guest editors for the symposium publication were
John A. Milner, The Pennsylvania State University, and Marcel
Roberfroid, Louvain University, Brussels, Belgium.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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1. Bloksma N., de Heer E., van Dijk H., Willers J. M. Adjuvanticity of lactobacilli. I. Differential effects of viable and killed bacteria. Clin. Exp. Immunol. 1979;37:367-375[Medline]
2. Conge G. A., Gouache P., Desormeau-Bedot J. P., Loisillier F., Lemonnier D. Comparative effects of a diet enriched in live or heated yogurt on the immune system of the mouse. Reprod. Nutr. Dev. 1980;20:929-938
3. De Dios Pozo-Olano J., Warram J. H., Jr, Gómez R. G., Cavazos M. G. Effect of a lactobacilli preparation on traveler's diarrhea. A randomized, double blind clinical trial. Gastroenterology 1978;74:829-830[Medline]
4. Deeth H. C., Tamine A. Y. Yogurt: nutritive and therapeutic aspects. J. Food Prot. 1981;44:78-86
5. DeSimone C., Grassi P. P., Bianchi-Salvadori B., Miragliotta G., Vesely R., Jirillo E. Adherence of specific yogurt micro-organisms to human peripheral blood lymphocytes. Microbios 1988;55:49-57[Medline]
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7. DeSimone C., Vesely R., Negri R., Bianchi Salvadori B., Zanzoglu S., Cilli A., Lucci L. Enhancement of immune response of murine Peyer's patches by a diet supplemented with yogurt. Immunopharmacol. Immunotoxicol. 1987;9:87-100[Medline]
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Perdigon G., de Macias M. E., Alvarez S., Oliver G., de Ruiz Holgado A. A. Effect of perorally administered lactobacilli on macrophage activation in mice. Infect. Immun. 1986;53:404-410
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, live-culture; 
,
pasteurized; 
, non-yogurt control. The non-yogurt control
group was significantly higher (P < 0.005) at each
time point; however, there was no difference over time among the
groups.