In this study we report a significant association between total intake of MUFA and skin photoaging in men but not in women. When the individual contribution of each source of MUFA was considered, higher intakes of MUFA from vegetable oil were however found to be negatively associated with severe skin photoaging independently of environmental factors known to cause premature and accelerated skin aging in both sexes, whereas intake of MUFA from animal products (dairy products, meat and processed meats) was not significantly associated with skin photoaging. In particular, a higher consumption of olive oil was inversely correlated with the severity of skin photoaging. Olive oil was the only one of the three vegetable oil sources of MUFA usually consumed in our study population (olive oil, sunflower oil and peanut oil) to present such a protective effect. These findings are consistent with previous studies which have addressed individual aspects of this relationship –. Hence, Purba et al.  reported a negative association between total MUFA intake, olive oil intake and skin aging, whereas Nagata et al.  found a positive association between MUFA intake and skin elasticity. In contrast, another study did not find any association between oleic acid consumption and wrinkled appearance and even reported a higher risk of senile dryness in higher consumers . However, in these two last studies, fatty acids were considered as a whole, without taking into account their specific origin.
The observed negative association between olive oil intake and severe photoaging may be due to its specific fatty acid profile with a high amount of MUFA and a low ratio of n-6 PUFA/n-3 PUFA , . Indeed, MUFA is far less susceptible to peroxidation than PUFA. In contrast to olive oil, we did not find dairy products to be negatively associated with skin photodamage although they provide comparably high amounts of MUFA to olive oil. However, dairy products are also a rich source of saturated fatty acids, which are known to be associated with insulin resistance and an increase of inflammatory processes . Another hypothesis would be that squalene and polyphenols contained in olive oils may play a role in preventing photodamage , . Squalene is to a large extent sequestered in the skin (sebum is reported to contain 12%), where it is believed to exert a major protective effect against free radical damage and skin dryness . Polyphenols are also known to be powerful radical scavengers. Both squalene and polyphenols have been assumed to be primarily responsible for the beneficial effects of the Mediterranean diet. Finally, as expected, the consumption of olive oil in our population was also positively associated with high consumption of fruits, vegetables, fish and tea, and negatively associated with sweet products, butter and milk. In that sense, the consumption of olive oil could also be considered as a marker of a healthy diet .
Our study has both strengths and limitations. The strengths encompass the assessment of dietary intake based on a mean of ten computerized 24-hour diet records in order to take into account weekly and seasonal intra-individual variability in the intake of the monounsaturated fatty acids, which may be considerable . Furthermore, a validated manual containing a photographic guide was provided to each subject in order to facilitate estimation of portion size among seven proposed portion sizes . Our study was also a well-characterized sample of middle-aged women and men living in the community evaluated. Finally, due to the number of statistical tests performed, we cannot exclude that some significant associations found may be due to chance, in spite of the overall coherence between findings in men and in women. Moreover, the cross-sectional design of our study does not allow us to address the causality of the associations observed.
In conclusion, our findings provide support for a beneficial role of olive oil in preventing severe facial photoaging. This result should be supported by further mechanistic studies taking into account the relationship between a diet rich in MUFA, subcutaneous fat and the overall aging process, of which skin photodamage may be a readily observable surrogate marker. Finally, our findings provide a useful insight into the beneficial effect of olive oil, as the main source of dietary fat, as promoted in a diversified diet, although the only way to demonstrate that olive oil can prevent photodamage is to perform an interventional study.