Fruit and vegetable (FV) intake has been recognized as an important component of a healthy diet and has become a key component of multiple national dietary guidelines, including those in China [1
]. Currently, the intake of vegetables by residents in China is gradually decreasing, and the intake of fruits remains low [3
]. Chinese dietary guidelines recommend that vegetables consumption should be 300~500 g/day, and that fruits consumption should be 200~350 g/day [4
]. However, according to the results of a sample of residents from 2010 to 2012, the average daily intake of vegetables and fruits for urban and rural residents in China is 269.7 g and 40.7 g, respectively [5
]. Only half of the Chinese population meet the criteria of fruit and vegetable intake recommended by the Chinese dietary guidelines [6
Past research on the relationship between food and human health has observed inadequate intake of fruits and vegetables to be among the top ten risk factors of death around the world [7
]. Vegetables and fruits are rich in vitamins, minerals, and dietary fiber, and low in fat, salt, and sugar. They play an important role in meeting the human needs for micronutrients, maintaining the normal function of the human intestines, and reducing the risk of chronic diseases. Fruits and vegetables also contain various plant compounds, organic acids, aromatic substances, and pigments, which can increase appetite, help digestion, and promote overall human health [8
Multiple studies have also shown that FV intake is closely and inversely associated with mortality. A nationwide Chinese study sampling more than 0.5 million adults aged 30–79 years concluded that fruit intake was associated with significantly lower mortality from several major vascular and non-vascular diseases [9
]. This point was also strengthened by a systematic review including 142 publications, concluding that FV intake was associated with reduced risk of cardiovascular diseases, cancer, and all-cause mortality [10
]. In Asian countries, the types of fruits and vegetables eaten or cooking methods may be different, hence this different FV profile might result in a disparate impact on health. In China, evidence to demonstrate that higher FV intake may be associated with significantly lower mortality from major cardiovascular disease and total mortality is limited [9
]. However, some mixed results and inconsistencies remain. Conversely, a recent study by Wang et al. found no confirmed association between FV intake and mortality [13
]. Until now, few studies have looked at a nationwide Chinese sample and investigated the association between both separate and combined fruit and vegetable intake and mortality. This study aimed to examine the association of combined FV intakes and separate fruit and vegetable intake with all-cause mortality utilizing data from a nationwide longitudinal sample.
To our knowledge, this is the first study, using a nationwide and all-adult sample in China, to explore the association of FV intake, both separately and combined, with all-cause mortality. The findings from our study have the potential to inform policy making and public health interventions on FV intake in China. In the present study, negative associations on mortality risk were observed, starting with the second quintile of intake (199 to ≤266 g/day of vegetables, 0 to ≤25 g/day of fruit and 225 to ≤300 g/day of fruit and vegetables).
Separate intake of vegetables or fruit was associated with reduced mortality from all-causes in all models. If participants consumed vegetables only, with the fully adjusted model, the greatest risk reduction effect of vegetables from all-cause mortality was shown in the amount of the fourth quintile (HR = 0.63, 95% CI: 0.53–0.76), which was about 327–408 g/day. When daily intake of vegetables by individual went beyond 408 g, the protection effect was attenuated by 27% (HR = 0.80, 95%CI: 0.67–0.96). The effect of single vegetable intake appeared to reach the threshold in the fourth quintile (327–408 g/day), beyond which there was no further reduction in mortality. This finding was also observed in combined FV intake; when people consumed fruit and vegetable together, it seemed that the lowest hazard ratio was in the fourth quintile (367–461 g/day) rather than the fifth quintile. These findings are in agreement with a meta-analysis conducted by Wang and his colleagues [17
]. They observed a dose–response relationship between fruit and vegetable intake and mortality up to a threshold of three servings/day for vegetables, and five servings/day for fruit and vegetables combined. There was no further reduction in mortality risk beyond these thresholds. Nguyen and his colleagues only observed a threshold of 3 to ≤5 servings for vegetables but not for fruit and vegetables combined [15
]. This is plausible because more intake of vegetables does not necessarily mean there are corresponding health benefits. The heavy metals in vegetables which often aggregate in the edible part is of growing concern in China due to the contaminated soils and irrigation water [18
]. Pesticide residue in vegetables is also a problem in China which was reported by Xu and her colleagues, showing that ~40% of collected samples tested positive for different kinds of pesticides and 6.1% exceeded the Chinese residue limits [19
]. Long term exposure to vegetables with heavy metals and pesticide residues is extremely hazardous to human health [20
]. High intake of vegetables increases the risk of exposure to these harmful substances which may counteract the benefits of vegetables.
Most participants in this study did not adhere to the amount of daily fruit intake recommended by Chinese Dietary Guidelines (200–350 g/day). The fourth quintile of fruit intake in this group of participants was only from 60 to 126 g/day, and more than 10,000 participants did not even take any fruit every day. The greatest mortality reduction of fruit was in the fifth quintile of intake, with hazard ratio equivalent to 0.24 compared to the first quintile (95% CI: 0.15–0.40). The protective effect of fruit seems to be superior to vegetables or FV combined. This may be due to the fact that more than 10,000 participants do not take any fruit; hence, this negative association with death is obvious once fruit is consumed and appears to be strong at maximum intake of fruit. The message to promote fruit intake in China still needs to be reinforced. At the same time, hazard ratios of fruit intake tended to decrease slightly with more intake of fruit (p for trend <0.001). A linear trend across the categories of fruit intake defined by five different quintiles is easily found which suggests that more fruit is advantageous to people’s health.
Intake of FV combined was inversely associated with all-cause mortality in this cohort of Chinese adults in the crude model. After adjustment for age and sex, the protective effect of FV combined was attenuated by about 31% with HR changing from 0.34 (95%CI: 0.28–0.40) to 0.65 (95%CI: 0.55–0.78). After further adding socio-economic, lifestyle, and health-related factors, the association was still consistent and statistically significant, while the protective effect of FV combined decreased by approximately 5% (HR changed from 0.65 to 0.70). It is worth noting that hazard ratios tended to decrease gradually accompanied with more intake of FV with p for trend <0.001. Obviously, there is a linear trend across the categories of FV intake defined by five different quintiles which is similar to fruit intake, as mentioned above. The results of the association analysis will also enable more evidence-based design of dietary policy interventions. This research could thus provide insights for policy makers and raise nutrition literacy awareness among the general population. WHO advocated eating at least 400 g of fruit and vegetables per day, while the third quintile of FV intake was even below 367 g/day which means that more than 60% participants in this cohort did not meet WHO standards. More efforts at promoting FV intake—particularly fruit intake—are needed as only a small proportion of Chinese adults currently meet Chinese and WHO recommendations for FV intake.
Findings from the present study are consistent with those from previous prospective cohort studies which have mostly found a significant inverse relationship between FV intake and all-cause mortality [16
]. A meta-analysis of global prospective cohort studies showed that pooled HRs of all-cause mortality were 0.95 (95% CI: 0.92, 0.98; p
= 0.001) for an increment of one serving a day of FV, 0.94 (95% CI: 0.90, 0.98; p
= 0.002) for fruit, and 0.95 (95% CI: 0.92, 0.99; p
= 0.006) for vegetables [17
]. In our study, the risk reduction effects of FV combined intake and individual fruit and vegetable intake levels were also observed as in the aforementioned study but were slightly stronger. In our study, the negative association with death of consuming both fruit and vegetables was slightly stronger than for separate intake of vegetables. The higher negative association of combined FV intake may be partly due to the fruit intake. Because large number of people in this cohort consume no fruit, the risk reduction in mortality due to fruit is comparatively obvious and strong even if people eat just a little more fruit. However, another recent meta-analysis showed reductions in risk of cardiovascular disease and all-cause mortality in those with a combined FV intake reaching up to 800 g/day, whereas no reductions in risk of cancer were observed for those with intakes above 600 g/day [10
]. These disparities in findings can be attributed to some factors that varied with studies of different designs, including measures of fruit and vegetable intake, covariates adjustment, follow-up time, and participants’ characteristics.
The main strengths of this study include large nationwide population sampling, which was conducted in municipalities with a range of substantially different geographies, economic development, public resources, and health indicators. This study was prospective, which minimizes bias and provides stronger evidence for causality. In addition, we used a cumulative intake of FV over the cohort period, which may reflect the long-term habitual patterns of dietary behavior. Finally, this study has used a 3 day 24-h recall as a detailed dietary method to reduce measurement error, which provided precise and accurate average values for calorie intake and for foods that are consumed every day such as vegetables, but this is not precise on the individual level regarding foods that are consumed only occasionally such as fruit in this cohort. Usually, food frequency questionnaires provide good differentiation between individuals with high and low consumption of infrequently consumed food, but the averages tend to be less accurate. In our context, we were able to find a difference between the vegetable data and the fruit data because we applied the 3 day 24-h diet data collection method. The higher accuracy of food diary method is a strength in our study.
The study also had several limitations. One limitation is that we did not have information on specific causes of death beyond all-cause mortality, which might be informative to test the association between FV intake and cause-specific mortality in the nationwide population. In addition, there may be some measured and unmeasured covariates that were not included in the analysis. Furthermore, there are many cooking methods and different types of FV; for example, raw vegetables are consumed more in western settings while cooked vegetables are consumed in eastern settings, which may have different implications for health and total mortality. These aspects were not reported on in this study. Finally, the different diet intakes may be indicators of different lifestyles, rather than reflecting effects of specific foods on health, so it is important for future studies to assess the different correlations with age, rural/urban, socio economic groups, and so on. Future studies could also consider including more detailed information of FV intake and linking to cause-specific mortalities.