An evaluation of dietary intakes and the appearance of skin aging among middle aged American women

The skin aging process is governed by a multitude of factors which include biological aging, influences of the environment, lifestyle choices, low body mass index, and menopause. Not only does aging affect how well our skin functions, it also determines how it looks. 

As the title suggests, this study is focused solely on the relationship between our diets & the way our skin looks i.e. our skin's appearance. This study does not concern itself with our skin's ability to function. For the purpose of assessing skin appearance, visual features of skin aging are defined as having a wrinkled appearance, senile dryness (age related dryness), skin atrophy (thinning).

Another point which distinguishes this study from previous research, is the sources of dietary nutrients being examined. While previous studies utilized nutritional supplementations, this study looked at nutrients purely from food sources.

The relevance of this study hardly requires elaboration. Obviously, we desire skin that looks moist & wrinkle-free. But more importantly, visible signs of aging such as wrinkles, irregular pigmentation, sagging, atrophy, elastosis (loss of elasticity) and telangiectasia (dilated blood vessels on surface of skin), have been proven in previous studies, to cause negative self esteem & social wellbeing {Bittergourd's comment: duh!}. Another study also linked "looking old for one's age" to an increased risk of mortality in individuals.

How was this study conducted?

The study sample consisted of 4025 American women aged between 40-74 years. Complete dermatologic evaluations of skin texture & colour, certain manifestations of aging, & all pathologic changes (signs of disease) were performed by dermatologists who underwent uniform training & followed standard protocols. To ensure consistency, random samples of these evaluations were further checked by a senior dermatologist.

For assessment of nutrient intakes, 24-hour diet recalls were administered to the women by trained dietary interviewers. Nutrient intakes for the foods were based on data obtained from the U.S. Dept of Agriculture. 

Since cigarette smoking plays such an established and major role in skin aging, it is important to capture and consider data on cigarette smoking. Hence, 1401 women were singled out as a subgroup for stratified analysis on cigarette smoking.

Here are some highlights on the skin appearance & characteristics of the women being studied:

There was significant correlation between wrinkles and senile dryness; as well as between senile dryness and skin atrophy. Women who possessed all 3 signs of skin aging were more likely to be white, have <12 years of education, low family income, postmenopausal, & had higher exposure to sunlight. Furthermore, skin atrophy associated strongly with lower BMIs; whereas a wrinkled appearance together with senile dryness appeared to be characteristics linked to women who were less physically active.

General findings of the study:

Distribution of nutrient intakes by skin-aging appearance.

Women with wrinkled appearance had significantly lower intakes of protein, cholesterol, phosphorus, vitamin A, & vitamin C in comparison with women without wrinkled appearances.

Women with senile dry skin had significantly lower intakes of linoleic acid & vitamin C than women without senile dry skin.

Women with skin atrophy also had significantly lower linoleic acid intake than women without skin atrophy.

Further analysis of each nutrient as it corresponds to skin appearance:

Overall, the study observed higher consumptions of vitamin C & linoleic acid, and lower consumptions of fats & carbohydrates in women with better skin appearances.

Vitamin C

A decreased vitamin C intake correlated with significant wrinkles and senile dryness. On a multivariate log adjusted scale, a 1-unit log increase in vitamin C intake decreased the chance of wrinkled skin by 11%, & decreased the chance of senile dry skin by 7%.

This is not surprising given that previous studies have shown vitamin C to play an active part in collagen synthesis, cell regeneration as well as wound repair. Vitamin C has also been found to possess strong antioxidant & photoprotective (having protective effect from ultraviolet light) properties on skin, hence its ability to improve wrinkled and dry skin.

Linoleic Acid

Similarly, increased consumption of linoleic acid was associated with decreased likelihood of the development of senile dry skin as well as atrophy of the skin. A 1-unit increment on the log scale corresponded to a 25% decrease in chance of wrinkles & a 22% decrease in chance of senile dryness & skin atrophy.

Linoleic acid is an essential polyunsaturated fatty acid (PUFA), a nutrient that is required for bodily functions & yet, it cannot be produced on our own. Therefore, it must be acquired through dietary intake. Once in our bodies, it can also be converted to other forms of PUFAs such as eicosapentaenoic acid (EPA) & decosahexaenoic acid (DHA), both of which are found in fish oil. 

Linoleic acid's beneficial effects on skin appearance, therefore, may lie in its ability to be converted to other PUFAs within the body. Besides, other research have already proven that a decrease in linoleic acid intake leads to the development of dermatitis, thereby evidencing the important role linoleic acid plays on the appearance of our skin.

{BG's comments: Some sources of linoleic acid include evening primrose oil, grapeseed oil, soybean oil}

Vitamin A

This study also found women with wrinkled appearances to have simultaneously lower intake of vitamin A. Again, this is not startling as previous research have already proven vitamin A to be an anti wrinkle agent & is currently being used as an ingredient in both topical as well as oral applications.

Dietary Fats & Carbohydrates

Perhaps the most interesting of all, is the new finding that elevated levels of dietary fats & carbohydrates correlated positively with skin aging. A 17g dietary fat increment, & a 50g carbohydrate increment, coincided with increments in multivariate adjusted odds ratios of having skin aging features. Although to date, this is the only study linking dietary fats & carbohydrates to skin aging, it has previously been established that higher Thiamine consumption led to wrinkled appearance. Thiamine is B vitamin that is commonly present in enriched cereal & grains. 

{BG's comments:

(1) a tablespoon of oil contains approx 16g of fats; 2 slices of bread contains approx 32g of carbohydrates; 1/2 cup dry rice contains approx 74g of carbohydrates.

(2) enrichment is the process of adding nutrients back to the products after such nutrients have been lost during the process of refinement.}

Results from analysis of the smoking subgroup:

A total of 1401 women were interviewed for smoking data. 38% of them were either current smokers or have previously smoked. 62% of them have never smoked.

Within smokers, those with wrinkled appearances were found to have consumed significantly lessor protein & niacin, compared with those with less wrinkles. In addition, higher calcium intakes were observed in smokers with skin atrophy compared with smokers without skin atrophy.

A few important points to keep in view when considering context of this study:

1. The sources of dietary vitamin C & linoleic acid might be important factors in influencing positive associations with skin appearance. At the time of this study, main sources of vitamin C in the U.S. are orange juice, citrus fruits, fruit juices & tomatoes. The main sources of linoleic acid are rapseed, soybean, green leafy vegetables & nuts. 
2. This study does not show direct causal link between the dietary nutrients & visual features of skin aging. 
3. The use of facial cosmetics & skin care were not factors for consideration in the study.
4. The 24-hour diet recall method for tracking nutrient intakes may not be a perfect reflection of an individual's long term diet, although effort was made to use trained interviewers so as to ensure accurate data collection as much as possible.

In Conclusion:

In spite of the study's shortcomings, it is an undeniable fact that dietary intake plays one of the most important roles in skin aging. Besides, the benefits we could reap from eating a skin friendly diet extend far beyond that which are only skin deep. Countless studies have proven that diets which are high in fruits, vegetables, fish & nuts are associated strongly with overall good health, so having good skin appearance is just the icing on the cake!!

( Source: Maeve C Cosgrove, Oscar H Franco, Stewart P Granger, Peter G Murray, Andrew E Mayes. (2007). Dietary nutrient intakes and skin-aging appearance among middle-aged American women. The American Journal of Clinical Nutrition. 86:1225-31; pp 1225-1231 )