THE CORRELATION BETWEEN PHYSICAL HEALTH AND MENTAL HEALTH

Transcription

1 HENK SWINKELS (STATISTICS NETHERLANDS) BRUCE JONAS (US NATIONAL CENTER FOR HEALTH STATISTICS) JAAP VAN DEN BERG (STATISTICS NETHERLANDS) THE CORRELATION BETWEEN PHYSICAL HEALTH AND MENTAL HEALTH IN THE NETHERLANDS AND THE US Introduction In this study the relationships between a mental health indicator which refers to negative mood and a number of health indicators with a more physical dimension are examined. In order to compare the results between the US and the Netherlands, the analyses have been carried out in both countries in a similar way. This type of international comparisons is useful for a number of reasons. Such comparisons indicate, for example, whether results are unique to a single population or whether consistent associations are evident in different countries. When similar results are obtained from different populations, one may be more confident in the validity of the findings. However, international comparisons are affected by a wide range of confounding variables, and definitive conclusions about, for example, the effectiveness of interventions to improve public health should be made cautiously. The Netherlands and US National Health Interview Survey The data used in this study are from the Netherlands Health Interview Survey 1990/1992 and from the US Health Interview Survey The National Health Interview Survey of Statistics Netherlands has been conducted continuously since 1981 to gather data on trends in health, life style and medical consumption in the Dutch population. Face-to-face interviews are used to obtain data on characteristics such as self-rated health, restricted activity, sick leave, consultations with general practitioners, specialists and dentists, hospital admissions and medication use. In addition to background information, data are obtained on health practices like smoking, alcohol use, physical activity and diet. These health practices questions are included in a selfcompleted, written questionnaire returned by the respondents after the interview. This self-completed questionnaire also contains questions on health indicators like for example the Affect Balance Scale. Data from the Netherlands Health Interview Survey may be somewhat biased by non-response, but it is difficult to establish the effect of the problem. The response rates are approximately 57% per year. About 75% of non-respondents are persons who refuse to participate and the next largest category are persons who were not at home and persons not able to answer. Comparisons of background variables of the Dutch Health Interview Survey with similar data from external sources indicate that the distributions of variables of the Dutch Health Interview Survey generally correspond rather well with results from other studies. Research on non-respondents on the Dutch Health Interview Survey indicated that they did not differ significantly from respondents with respect to the variables of primary interest. Respondents are assigned a weight variable that adjusts for non-response and other types of selection bias, and the weighted 1

2 distribution reflects accurately the population of the Netherlands. The sample sizes for respondents of all ages are about 9,000 individuals each year. The U.S. National Health Interview Survey is a household survey in which information on the health and health related topics of the US resident population is gathered. The Health Promotion and Disease Prevention (HPDP) supplement of the 1991 US National Health Interview Survey (NHIS) included a number of questions on negative mood. One adult per family was randomly selected from the full NHIS sample for a personal interview with this Health Promotion questionnaire. A total of 43,732 adults 18 years of age and older responded tot the 1991 NHIS-HPDP. The overall response rate was 87.8%. Self-response was required for all questions in the HPDP questionnaire (Jonas & Wilson, 1997). The Affect Balance Scale In the US National Health Interview Survey of 1991 and in the Dutch Health Interview Survey since 1989, 5 items of the Affect Balance Scale are included. This Affect Balance Scale has been developed by Bradburn in the late sixties and is meant to measure positive and negative aspects of mental wellbeing at the level of the population. Five items of this scale measure positive mental wellbeing and five items refer to negative mental wellbeing. In the US and the Dutch Health Interview Surveys only the five negative items of the Affect Balance Scale are included. With these five items psychosocial complaints like loneliness, restlessness, being bored, being depressed, and being upset are measured. In annex 1 the exact questioning of the Affect Balance Scale in both Health Interview Surveys is presented. The wording of these five questions is rather similar in both countries, but the answer categories differ somewhat. In the US questions there are five instead of four answer categories. The answer category "rarely" is not included in the Dutch situation (see annex 1). In order to facilitate proper comparisons between the American and the Dutch situation respondents in both countries were assigned a score based on the answer category on each ABS-item. The scores on each item range from 1 for the category 'never' to 4 for the category 'very often'. In the US the category "rarely" was coded proportionally distant to the percentage of the responses in the categories "never" and "sometimes". So, the actual score of this category differs somewhat per ABS-item. By adding the scores on the five items respondents were assigned a total score, ranging from at least 5 to a maximum of 20. Next step was the division of the population distributions of both countries into three groups. We chose for a division into persons with a high, middle, and a low score. Persons in the upper 6 to 8% of the divisions are called persons with high negative mood, persons in approximately the next 23% of the division are called persons with middle or average negative mood and the other 70% of the respondents are persons with low negative mood. At this point we have to admit that these cut off point are chosen arbitrarily and are useful for comparison reasons only. Table 1 In table 1 some basic results from the Dutch Health Interview Survey are presented. According to our definition of high negative mood about 6% of the Dutch population report high negative mood, about 23% report middle negative mood and about 72% report low negative mood. The number of women with 2

3 high negative mood is about twice as high as in men: 3.8% in men and 7.6% in women. However, after adjustment for differences in the other background characteristics the difference between men and women reduces to about 2% (see table 2). Table 2 With respect to age, it showed that the relationship has reversed after adjustment: the unadjusted percentage among older persons is higher than among younger persons; after adjustment the percentage among older persons is lower (see table 2 and graph 1). There also is a strong relationship between negative mood and income: the percentage in the lowest category is almost twice as high as the percentage in the highest income group. The same relationship holds for level of education: the figures in the lowest education group are much higher than in the highest education group. The strongest relationship is found between negative mood and marital status beta=0.12). The lowest percentage is found among married persons, and the highest percentage is found among widowed and divorced persons. Analysis of widowed and divorced persons separately showed no difference between the percentages of these groups. The last characteristic shows a significant relationship between negative mood and paid job. Among persons without a paid job the percentage with high negative mood is somewhat higher than the percentage among people with a paid job. Table 3 In table 3 the results of a number of multiple classification analyses are presented. The table shows the relationships between high negative mood and a number of other rather physical health indicators before and after adjustment for differences in gender, age, income, education, marital status, and paid job. This means that differences between the distinguished groups within the presented health indicators are not due to differences in gender, age, income, education, marital status or paid job. All of these health indicators, except both Body Mass Indices, show a significant (p 0.05) correlation with negative mood. The strongest relationship is found among perceived health and negative mood (beta=0.20). From the persons with a perceived health "less than good" about 14.7% report high negative mood after adjustment; from the persons with a good perceived health only 3.4% report a high negative mood. From the persons who had to cut down their activities 11.8% report high negative mood; among persons who didn't need to cut down their activities only 4.8% report high negative mood. Among the other health indicators presented in table 3 almost the same patterns are visible as with perceived health and "temporary cut down of activities". The overall picture in this table is that these more or less physical health indicators are strongly related to negative mood. However, these cross sectional data do not allow to draw conclusions on the way the mental health indicator is related to physical health: does negative mood cause bad physical health or does bad physical health cause negative mood? 3

4 Table 4 If we look more in detail into the type of chronic conditions respondents are suffering from, we see per condition almost the same pattern as with the overall indicator in table 3. In the Dutch Health Interview Survey respondents are asked for 24 specific chronic conditions of which 22 are significantly (p0.05) correlated with negative mood. With respect to these chronic conditions it can be said that these in general show a rather strong physical dimension. Table 4 shows the relationships of these chronic conditions with negative mood. The strongest relationship is found in "dizziness with falling" (beta=0.11). After adjustment for differences in gender, age, education, income, marital status and paid job the percentage of persons reporting high negative mood among persons suffering from "dizziness with falling" is almost 22%; among persons not suffering from "dizziness with falling" the figure is 5.4%. The next strongest relationship is in migraine (beta=0.08). The number of persons with high negative mood among persons suffering from migraine is more than twice as high as among persons not suffering from migraine. All other chronic conditions show roughly the same kind of relationship with negative mood as these two: a bad score on the chronic condition correlates with a high percentage of persons reporting high negative mood. Table 5 In table 5 the results of the questions on a number of physical disabilities, as included in de Dutch Health Interview Survey, are presented. These questions are rather objective measures for long term hampering of physical functioning. All items presented in this table correlate significantly (p0.05) with negative mood. The strongest relationship with negative mood is found in the item referring to mobility. In the Dutch Health Interview Survey respondents are asked whether they have problems in "walking 400 meters without resting". Among people who can't walk 400 meters without resting (including the answer category "with major difficulty") 19.0% report high negative mood. Among people without mobility problems (including the answer category "with minor difficulty") only 5.1% report high negative mood. Next strongest relationship refers to persons having "difficulty carrying a heavy object of 5 kilos for 10 meters, like for example a full shopping bag". The percentage among persons who can't carry a heavy object is 3 times as high as among persons having no problems in carrying a heavy object. If we look into persons reporting problems in "bending down and picking up something from the floor", we see that 16.7% report high negative mood. Among persons not reporting problems in bending down the figure is 5.3% only. The other physical disability items refer to hearing and sight problems. All of these items also correlate rather strongly with negative mood. The Netherlands and the US compared. After we have pointed at the statistical relationship between physical and mental health at the level of the total population, we should find out whether this relationship is unique for the Netherlands, or whether this relationship is consistent among other countries. It is possible that this relationship is culturally 4

5 determined and that in other cultures physical health and mental health do not correlate in the same manner as in Western cultures. In order to find out if this relationship is consistent in the Western culture a number of similar analyses are applied on the Dutch and American data. Apart from the Affect Balance Scale five other health indicators are suitable for comparison between the two countries. These five health indicators all refer to physical health mainly. Table 6 In table 6 the results on the comparison between the US and the Netherlands are presented. In order to achieve more proper comparisons between both countries we used Odds Ratios after adjustment for confounding variables as gender, age, education, income, marital status, and paid job. First health indicator listed in table 6 refers to the Body Mass Index of 30 and over. In the Netherlands the Body Mass Index is not significant correlated with negative mood, but the results tend to show the same relationship as in the US. The estimate from the United States is somewhat higher than the Odds Ratio of the Netherlands. Next health indicator refers to perceived health. In both the United States and in the Netherlands the Odds Ratios differ significantly from the reference group. The Odds Ratio of the Netherlands is much higher than the Odds Ratio of the United States. This is probably caused by the way perceived health is asked for in both questionnaires. Both answer categories of the United States and the Netherlands exist of 5 items, but in the American Health Interview Survey only 2 answer categories refer to a perceived health less than good, while in the Netherlands 3 answer categories refer to a perceived health less than good. As a consequence about 13% of the American population report their health as less than good, while this number in the Netherlands is about 20%. It is likely that these different distributions will have implications on the estimated Odds Ratios. The Odds Ratios of the next indicator -the limitations of activities- point at almost similar relations in both countries. In both countries hypertension is significant related to negative mood. The magnitudes of the Odds Ratios are almost the same in both countries. With respect to diabetes, only in the United States this chronic condition is significantly related to negative mood. The results of the Dutch Health Interview Survey show no significant relationship, but as in the Body Mass Index the Dutch Odds Ratio tend to show the same relationship as in the US. Discussion From the presented relationships between a mental health indicator -the Affect Balance Scale- and a number of health indicators referring to a more physical dimension of health, we can conclude that physical and mental health are rather strongly correlated. In general, these relationships show rather similar magnitudes and directions in both the Netherlands and the USA. As mentioned before, it is hard to establish the direction of the relationship on the basis of these cross sectional data: does negative mood cause or contribute to physical complaints, or are physical complaints responsible for high negative mood at the level of the population? 5

6 Some of the complaints we looked at, suggests that bad physical health causes mental health problems. For example, it is not likely that high negative mood causes or contributes to spinal affections. On the other hand it is evident that high negative mood can contribute to physical complaints like for example hypertension, migraine, or heart diseases. In many cases, however, it is plausible that there is a mutual influence between physical health and mental health. Literature Jonas, BS & RW Wilson, Negative mood and urban versus rural residence: using proximity to metropolitan statistical areas as an alternative measure of residence. Advance Data, nr 281. NCHS. 6

7 Annex 1 Questions on the Affect Balance Scale Netherlands Health Interview Survey Have you felt very lonely or abandoned at any time in the past few weeks? Have you felt so restless at any time in the past few weeks that you could hardly sit still? Have you felt bored at any time in the past few weeks? Have you felt depressed or felt very low about something at any time in the past few weeks? Have you been upset at any time in the past few weeks because of something someone said about you? Never Sometimes Often Very often U.S. National Health Interview Survey During the past 2 weeks: How often have you felt very lonely or abandoned? How often have you felt so restless that you could hardly sit still? How often have you felt bored? How often have you felt depressed or felt very low about something? How often have you felt upset because of something someone said about you? Never Rarely Sometimes Often Very often 7

8 Graph 1. Adjusted1) percentage of persons with high negative mood by age, Neth. Health Interview Survey 1990/ % years years years years years 65+ years 1) Adjusted for differences in sex, education, marital status, and paid job. 1) Adjusted for differences in sex, education, marital status, and paid job.

9 Table 1. Negative mood (ABS) and other respondent charcteristics (persons 16+ years), Neth. HIS 1990/1992. Negative mood High Middle Low % Total Gender Age Income Education male female years years years years years years low middle high unknown low middle high Marital status married never married widowed/divorced Paid job yes no

10 Table 2. High negative mood (ABS) and some background characteristics, Neth. HIS 1990/1992. High negative mood unadjusted eta adjusted 1 beta % Total 5.8 Gender Age Income Education male female years years low middle high unknown low middle high Marital status married never married widowed/divorced Paid job yes no ) Each characteristic adjusted for the other characteristics.

11 Table 3. Negative mood (ABS) and other health indicators (persons 16+ years). Neth. HIS 1990/1992. high negative mood unadjusted adjusted 1 beta % P Perceived health less than good yes no Temporary cut down of activity yes no Temporary confined to bed yes no or more chronic conditions yes no or more physical disabilities (OECD) yes no or more limitations of daily activities (ADL) 2 Body length Body Mass Index >=27 Body Mass Index >=30 yes no < 168 cm cm >177 cm yes no yes no Adjusted for differences in age, sex, education, income, marital status, and paid job 2. Persons 55+ years.

12 Table 4. High negative mood (ABS) and some chronic conditions (persons 16+ years), Neth. HIS 1990/1992 high negative mood P unadjusted adjusted 1 beta % Asthma, chronic bronchitis yes no Perinasal, frontal or maxillary sinusitis yes no Serious heart disease or heart attack yes no Hypertension yes no Stroke and effects of stroke yes no Stomic ulcer/ duodenal ulcer yes no Disorder of the larger or the small bowel yes no Gall-stones or inflammation og gall-bladder yes no Disease of the liver, liver cirrhosis yes no Stones in the kidney yes no Serious disease of the kidney yes no Chronic cystitis yes no Diabetes mellitus yes no Thyroid trouble or goitre yes no Chronic spinal affections yes no Arthrosis of knees, hips or hands yes no Arthritis of hands or feet yes no Other chronic arthritis yes no Epilepsy yes no Dizzyness with falling yes no Migraine yes no Serious skin disease yes no Malignant neoplasm or cancer yes no Adjusted for differences in age, sex, education, income, marital status, and paid job

13 Table 5. High negative mood (ABS) and some physical disabilities (persons 16+ years), Neth. HIS 1990/1992. high negative mood unadjusted adjusted 1 beta % P Can you hear what is said in a group of 3 or more persons yes no Can you carry on a conversation with one other persons yes no Is your eyesight good enough to read the small letters in the newspaper yes no Is your eyesight good enough to recognize someone's face at a distance of 4 metres yes no Can you carry an object of 5 kilos for 10 metres, for example a full shopping bag yes no Can you, when standing, bend down and pick up something from the floor yes no Can you walk 400 metres without resting yes no Adjusted for differences in age, sex, education, income, marital status, and paid job

14 Table 6. Adjusted Odds Ratios for high negative mood in the USA (1991) and the Netherlands (1990/1992). BMI >30 Adjusted odds ratio C.I. USA 1.22 ( ) Netherlands 1.13 ( ) Perceived health less than good USA 3.11 ( ) Netherlands 4.97 ( ) Temporary cut down of activity USA 2.67 ( ) Netherlands 2.68 ( ) Hypertension Diabetes USA 1.47 ( ) Netherlands 1.53 ( ) USA 1.61 ( ) Netherlands 1.36 ( )