Physiological and psychological changes associated with old age influence the health of aging populations, as well as their food consumption and subsequent nutritional status [1]. Chronic diseases are also more prevalent in this population than in younger adults and are thought to impact food choices, healthy eating and nutrient intake. Older people are also susceptible to malnutrition because of pre-existing multiple chronic diseases. Seasonal variations in food consumption and associated physiological changes can differ because of the tendency to contract chronic diseases and the existence of multiple chronic diseases [2]. In previous studies, seasonal changes reportedly affected the emotional state, appetite (hormonal state), seasonal food manufacturing (especially fruits and vegetable), food cost and consequently food consumption of people, but no specific data have been published regarding elderly individuals [34]. Variations in food consumption can be determined by measuring energy consumption and nutrition intake as well looking at as serum/plasma parameters to determine seasonal nutritional status [4]. However, there is limited evidence regarding seasonal changes, food accessibility, food choice and consumption among people of old age [34]. Therefore, it is important to evaluate nutritional status in the elderly who might be at higher risk of malnutrition [16]. Thus, this study was conducted to investigate seasonal changes in energy intake in older adults and to explore the associated factors.

Free living participants aged 65 years or over residing in Ankara province, Turkey were enrolled in this single center prospective study (male: 11, female: 20). Inclusion criteria were having sufficient cognitive and functional ability to adapt to and understand the study procedures (with cognitive tests), residing in the same region for at least the last three years, and willing to take part in the study. Participants were asked to sign the informed consent form and reminded that they could withdraw any time without citing any reasons.

Exclusion criteria were receiving hospital treatment (or being bed bound at home), having memory and speech disorders, cancer, traumatic disease (such as associated with an accident), swallowing disorders (such as dysphagia), difficulties in accessing and preparing food, receiving enteral/parenteral nutrition (at home or hospital), and taking vitamins and or mineral supplements. The study protocol was approved by the ethics committee of Gulhane Military Medical Academy, Turkey (Number: 13/1,648.4-1,242). Biochemical analyses were conducted under the project with the support of the Hacettepe University Scientific Researches Unit (Number: 2014/27-1).

A total of 43 individuals were initially enrolled, but two passed away during the study and another ten withdrew consent. Among the 31 remaining subjects, 20 (65%) were female and the mean ages were 73.9 ± 7.0 and 75.5 ± 5.7 years for females and males, respectively. Additionally, the mean education years were 6.2 ± 4.4 years in females and 10.4 ± 5.9 years in males. The number of individuals with self-reported diseases was 19 in females and 8 in males. Additionally, nine females and four of males reported a current diet therapy for any reason (e.g., reducing diet, diabetes or cardiovascular system diseases). The mean BMI value was found to be 29.8 ± 2.5 kg/m² and 32.5 ± 3.8 kg/m² in males and females, respectively. Additionally, 55% and 27.3% of female and male participants, respectively, reported that emotional state affected their food consumption. Approximately 45.5% of females and 66.7% of males reported reduced food intake when experiencing sadness, and 25% of females and 18.2% of males reported increased food intake when experiencing happiness (Table 1).

Occurrence of physiological and psychological changes across seasons is well known. While younger adults easily adapt to seasonal changes, older adults may have difficulty in doing so, which makes them vulnerable to different stressors [12]. In this study, food consumption varied seasonally, and this was accompanied by alterations in energy and nutrient intakes as well as the blood levels of nutritional parameters.

Seasonal changes also impact emotional states and food consumption in all age groups [13]. In this study, most older adults who thought their emotional state affected their food consumption (45.5% of females, 66.7% of males) ate less under emotional distress, while during times of emotional happiness their well-being increased, as did their food intake (25.0% of females, 18.2% of males). This is an interesting finding as most studies have reported increased cortisol because of stress causes leptin resistance, leading to increased food consumption [1415]. In addition to emotional changes, changes in food consumption depend on access to certain foods during different seasons [1617]. In the present study, participants preferred consuming foods rich in fat and carbohydrates during winter, resulting in higher energy consumption. On the other hand, cultural background and knowledge as well as seasonal variations in food availability can unintentionally influence preparation of meals by impacting the use of fat or carbohydrates.

Similar studies by Cai et al. [17] and Smolková et al. [18] reported a significant increase in fresh vegetable and fruit intake, which doubled in summer and autumn in comparison to winter in accordance with reports from other regions across the country. However, in the present study, fruit consumption only increased in autumn and decreased in spring in males. This may be related to, at least in part, increased availability of fresh fruit and vegetables throughout the year in the region, as well as their lower costs. Seasonal changes in food consumption in older adults also led to variations in their energy and nutrient intakes in this study. When compared to winter, females and males consumed 343 kcal/day and 577 kcal/day less energy, respectively, during summer, which was likely related to higher macro nutrients in winter. Intake of most nutrients was also higher in winter, but these differences were not significant. Moreover, the increases in some nutrients were found to be parallel to seasonal food consumption. The finding that energy and protein intake were reduced in summer and autumn should be investigated further to determine if there is a risk of under nutrition. Insufficient nutrient intakes were found in both genders, and two-thirds of male participants enrolled had insufficient fiber intake in spring compared to the other seasons. Lower consumption of oilseed, legumes or fruits in spring might explain this. In males, insufficient magnesium intake was found during all seasons except winter (Table 3). Like many previous studies of elderly individuals [1920], consumption of milk and dairy products was below the recommended levels in all seasons, potentially leading to insufficient intake in calcium and phosphorus. Because calcium, magnesium and vitamin D are important nutrients for healthy bones, our findings emphasize the need to increase awareness of sun exposure and to add more dairy products to the diets of older individuals. Moreover, reduced n-3 fatty acid intake in summer may occur to decreased availability of fish, which also deserves attention given that Turkey is a Mediterranean country. In the present study, the amount of salt consumption was not recorded. Rather, only the sodium content of food was calculated. For both sexes, sodium intake increased in winter (P < 0.05). In Turkey, bread is the main source of sodium according to the national food survey consumption. Therefore, increases in sodium may be explained by higher consumption of bread during winter.

Olmedilla et al. [21] and Rautalahti et al. [22] demonstrated that there were variations in blood parameters of some nutrients, vitamins and antioxidants in different seasons in adults. In a sample of Chinese people younger than 65 years of age, folate insufficiency was 48.0% in spring, but 26.2% in summer and autumn, and serum folic acid levels in males increased in winter but decreased in summer [23]. However, in the present study, consumption of any type of food was not found to be related to plasma folic acid level. Indeed, unless restored artificially, blood levels of fat soluble vitamins may not be determined by intake from natural sources such as legumes, oilseed, vegetables or meat.

Vitamin D deficiency is common in the elderly and related to chronic diseases such as diabetes, depression, etc. [24]. In the present study, serum PTH levels in winter and spring, as well as plasma vitamin D levels in spring were higher than in other seasons. Vitamin D levels were highest in autumn, which is in accordance with the results of previous studies across various population groups [2425] because of the potential influence of temperature and sunlight. In the same region, vitamin D deficiency was previously found in 40.1% of nursing home residents and 24.4% of community dwelling older adults, most of whom had multiple chronic conditions [25]. None of the study participants were taking nutritional supplements before enrollment or during follow-up. As a result, we observed significant variations in plasma vitamin D levels over the 12-month period. Plasma retinol level increased in autumn when compared to other seasons, while variations in vitamin C level did not reach statistical significance. Nevertheless, total fruit and vegetable consumption strongly correlated with serum vitamin C level as in previous studies [56]. Moreover, because long term supplementation of vitamin E, vitamin C and β-carotene did not reduce mortality in a prospective study [26], seasonal variations in blood levels of vitamins and minerals may be adaptive and should not always be considered as illness. The best approach could be to encourage older adults to consume sufficient amounts of fresh fruits and vegetables during every season. The average amount of vegetables and fruit consumed by individuals during the study met the daily vegetable and fruit consumption recommended by the WHO [27] for people 65 years or older (400 g/day). The percentage of the individuals consuming more than 400 grams of total fruits and vegetables was 38.7% in winter, 77.4% in spring, 64.5% in summer and 54.8% in autumn. These numbers suggest that older adults should be encouraged to increase their fruit and vegetable intake from autumn to winter.

In conclusion, energy and nutrient intake and blood levels varied across seasons in older adults. This study did not include nursing home residents or those who are not functionally independent. Also, older adults included in this study had better socio-economic status and eating conditions than the general Turkish society. However, even wider seasonal variations can occur in elderly with disabilities who have limited access to food. Future studies are required to evaluate the potential for improvements in care of older adults through modification of diets by nutritionists according to seasonal variations as well as periodical reviews of individual eating patterns, food sources and environmental factors.